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The world recreated: Redating Silbury Hill in its monumental landscape

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A classic exposition of the difficulties of dating a major monument and why it matters. Silbury Hill, one of the world's largest prehistoric earth mounds, is too valuable to take apart, so we are reliant on samples taken from tunnels and chance exposures Presenting a new edition of thirty radiocarbon dates, the authors offer models of short- or long-term construction, and their implications for the ritual landscape of Silbury and Stonehenge. The sequence in which monuments, and bits of monuments, were built gives us the kind and history of societies doing the building. So nothing matters more than the dates...
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The world recreated: redating Silbury
Hill in its monumental landscape
Alex Bayliss1, Fachtna McAvoy2& Alasdair Whittle3
A classic exposition of the difficulties of dating a major monument and why it matters. Silbury
Hill, one of the world’s largest prehistoric earth mounds, is too valuable to take apart, so we
are reliant on samples taken from tunnels and chance exposures. Presenting a new edition
of thirty radiocarbon dates, the authors offer models of short- or long-term construction, and
their implications for the ritual landscape of Silbury and Stonehenge. The sequence in which
monuments, and bits of monuments, were built gives us the kind and history of societies doing
the building. So nothing matters more than the dates . . .
Keywords: Europe, Late Neolithic, Early Bronze Age, Beaker, ritual landscape, radiocarbon
dating, Silbury Hill, Stonehenge
Introduction
There came a time in many past societies when prodigious amounts of labour were directed
into great tasks of construction, and few parts of the world are without mounds, pyramids,
ziggurats or other substantial earthworks of some kind. Some of these are historically late,
such as the mounds of the Mississippian culture, which was at its peak in the period
AD 1200-1400. Others go back much earlier, such as the temple platforms of Mesopotamia
from the fifth to the fourth millennia BC, followed by the ziggurats of the third millennium,
or the first pyramids in Egypt, the earliest of which is the Step Pyramid of Djoser at Saqqara
(after 2686 BC, the start of the Third Dynasty) (summarised in Whittle 1997a: 143-4;
with references). No one sequence is quite the same, and these massive undertakings were
often preceded by smaller enterprises. This sense of change and the scale which developed
monuments can reach have prompted many questions. Who thought up these investments?
What imperatives drove them? Whose social and political interests did they serve? Did they
recurrently appear at significant points in sequences?
The Late Neolithic in southern Britain, broadly speaking in the third millennium BC,
is one example of a society which engaged in enterprises of this kind, though not quite on
the scale of some of the most extravagant examples worldwide. Impressive constructions in
timber, earth, chalk and stone were numerous, but mostly grouped into local complexes, the
best known spread across central-southern England (or Wessex) (Renfrew 1973; Wainwright
1English Heritage, 1 Waterhouse Square, 138-142 Holborn, London EC1N 2ST, UK
2English Heritage, Fort Cumberland, Fort Cumberland Road, Eastney, Portsmouth PO4 9LD, UK
3Cardiff School of History and Archaeology, Cardiff University, Humanities Building, Colum Drive, Cardiff CF10
3EU, UK
Received: 5 April 2006; Accepted: 21 July 2006; Revised: 4 August 2006
antiquity 81 (2007): 26–53
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Alex Bayliss, Fachtna McAvoy & Alasdair Whittle
1989). The earthwork enclosures (‘henges’) of Avebury and Durrington Walls, containing
substantial internal settings of stone and timber, and Stonehenge itself, are prime examples.
Clearly these were collective undertakings, in that vast amounts of labour were needed,
but how was this mobilised and who, if anyone, directed it? Compared with earlier
constructions in the fourth millennium such as long barrows, causewayed enclosures and
cursus monuments, what does the change of scale signify?
Many answers have been given to these sorts of questions, which we will return to below.
Much is at stake, in terms of the kind of society and the pace and trajectory of change
which we envisage at this time. Perhaps all answers so far – and perhaps all the questions too
– have been offered within a rather loose or imprecise chronological framework. Material
culture studies and individual site sequences offer some sense of order, but radiocarbon
dating in this period has usually relied on small numbers of samples, often poorly selected,
the results of which have normally been examined informally (cf. Bayliss et al 2007a). Only
the chronology of Stonehenge itself has been explicitly modelled (Cleal et al. 1995: 511-35;
Bayliss et al. 1997; Bronk Ramsey & Bayliss 2000), and as we shall see below, other readings
are possible. This lack of chronological precision means that, whatever interpretive camp we
may belong to, monuments tend to be lumped together (for an honourable exception, see
Garwood 1991). What potentially may have been varied sequences structured by dramatic
events, gaps, resumptions, accelerations and decelerations, have not so far been seen, both
because we have not been willing to engage with chronology and because the now available
methodology which can serve to redress the situation has not yet been consistently applied.
Silbury Hill is a case in point. Despite a long history of investigation and a general
ascription to the Late Neolithic, the monumental mound has never been reliably dated.
Recent disturbance to the mound, however, has allowed the collection of new samples, and
other samples have been obtained from the archive. Thirty radiocarbon measurements are
now available, which we interpret within a Bayesian statistical framework. From this, we
present two chronological models. These agree in suggesting a date in the third quarter of
the third millennium cal BC for the construction of the primary turf mound. Alternative
readings are presented for the later history of the monument. In one, the mound is seen as
a sequential series of constructional episodes and does not take on its completed form until
the turn of the third millennium; in the other, construction is a much swifter process and the
mound is essentially completed during the third quarter of the third millennium. Neither
model is entirely satisfactory, but we feel that a more extended process of construction
conforms better to our existing data. We then go on to discuss the implications of this for
our understanding of the regional sequence and beyond, including comparison with the
sequence at Stonehenge and the appearance of Beakers. We have the methodology now to
offer much more precise estimates of date and we should be much more ambitious in our
efforts to apply this to the Late Neolithic in southern Britain – and elsewhere.
Silbury Hill
The monumental mound of Silbury Hill sits on the edge of the upper Kennet valley,
Wiltshire, close to the Avebury henge, the West Kennet Avenue, The Sanctuary, the West
Kennet palisade enclosures and the West Kennet long barrow (SU 100 685; 51.24.56N,
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Redating Silbury Hill in its monumental landscape
Figure 1a. Silbury Hill from the north-east (NMR 21810/24 c
English Heritage, NMR).
01.51.25W; Figures 1a & 1b). It is thus part of one local complex, others lying to the
north in the upper Thames valley and to the south at intervals across the Wessex Chalk
(Wainwright 1989). Despite a long, punctuated history of investigation from the eighteenth
to the twentieth centuries, and a general ascription to the Late Neolithic, Silbury Hill has not
so far been reliably dated (Whittle 1997a). How therefore does it relate to the construction
of Avebury and other local monuments, or further afield to Stonehenge?
We know, especially from the excavations of Richard Atkinson in 1968-70, that Silbury
Hill was developed from a layered and perhaps stake-revetted primary mound by the addition
of prodigious amounts of chalk, derived from flanking quarries and ditches, to reach its final
dimensions of around 160m in diameter and 40m in height (some 30m above the buried
old land surface). No clear evidence was recorded in the Atkinson excavations for prolonged
breaks in the process of construction, in the form of major or developed turflines (Whittle
1997a: 25), and there are none in the six vertical cores through the mound obtained in
2001-2003 (see below). While arguing that construction was a single process, Atkinson
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Alex Bayliss, Fachtna McAvoy & Alasdair Whittle
Figure 1b. Diagrammatic section through Silbury Hill.
(1968; 1970; 1978) suggested three major stages in its development (I: primary mound; II:
first chalk enlargement; and III: final chalk enlargement; summarised in Whittle 1997a: 26;
Figure 1b). Whittle suggested a series of more individual constructional events or phases
(a-l: Whittle 1997a: 25) and the possibility of a lengthier span over which construction took
place, over ‘one or more generations’ rather than the decade or so envisaged by Atkinson.
The four radiocarbon dates obtained using non-experimental methods on material from
the 1968-70 excavations suggested a date in the third millennium cal BC (Figure 2), thus
placing the monument in a Late Neolithic context rather than an early Bronze Age one
which had been previously considered plausible. It was not, however, possible, on the
samples available (and see below), to do more than suggest a date for construction between
‘2800/2500-2400/2000 BC’ (Whittle 1997a: 26).
The programme reported here sought to redress both these uncertainties, over the date
of construction and the span of construction.
Previous dating
Ten radiocarbon measurements had been obtained previously (Whittle 1997a: Table 1;
Table 1; Figures 2 & 3). Two were obtained in the late 1960s from Isotopes Inc., New Jersey.
One of these (I-2795) was made on a mixture of antler fragments from the 1867 and 1922
excavations in the flank of the mound on its eastern side (Atkinson 1967: 262). As these
antlers may have been of a range of actual ages, this result does not provide an accurate
date for the chalk mound. A second bulk sample, consisting mainly of unburnt fragments
of hazel with a small quantity of the roots and stems of other plants, was collected from the
turves of the primary mound (I-4136; Atkinson 1969). This was pretreated and dated by
gas proportional counting of carbon dioxide according to methods outlined in Walton et al.
(1961), Trautman and Willis (1966), and Buckley et al. (1968).
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Redating Silbury Hill in its monumental landscape
Figure 2. Calibrated radiocarbon dates from non-experimental radiocarbon measurements from Silbury Hill available in
1997.
Figure 3. Calibrated radiocarbon dates from different fractions of the turves used to build the primary mound.
Another series of measurements was undertaken on the turves of the primary mound,
as part of an experimental programme at the Smithsonian Institution to determine the
feasibility of dating prehistoric earthworks by dating turf buried during construction.
Insoluble organic matter of different particle sizes was dated after hot alkali and acid
pre-treatment (Stuckenrath & Mielke 1973), and alkali-soluble fractions were also dated
from two of the samples (Table 1; Figure 3). This was done using gas proportional counting
of methane (Sigalove & Long 1964). Only one of these results is statistically inconsistent
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Alex Bayliss, Fachtna McAvoy & Alasdair Whittle
Table 1. Radiocarbon results from Silbury Hill.
Calibrated date Posterior density
Laboratory Radiocarbon range (95%) estimate (probability)
number Material and context age (BP) δ13C() Weighted mean (BP) confidence (see Figure 4)
Oldlandsurface
OxA-13211Sample 4 (Bone 690 find 433),
indeterminate mammal bone,
sheep/goat size, from the old land
surface below the primary mound
(0.87E, 1.31N-1.26N, at eastern
edge of ‘pit’ or disconformity in
layers at base of the primary
mound: Whittle 1997: 20)
2792 +
34 20.4 1020-840 cal BC -
OxA-13333Sample 5, proximal pig radius
(Bone 559 find 241), from old
land surface at ring 4 of western
lateral tunnel, in area of primary
mound (Whittle 1997: Figure 12)
3916 +
28 20.8 3944 +
24 (T=3.5;
T(5%) =3.8; ν=1)
2550-2345 cal BC 2550-2535 cal BC
(1%) or 2495-
2340 (94%)
GrA-27332 Sample 5, replicate of OxA-13333 4015 +
45 21.4
Primary mound
I-4136 Small twigs, hazel from bark
(excavator’s identification), and
plant stems and roots, from
surfaceofturvesincoreof
primary mound; all unburnt
material
4095 +
95 2900-2450 cal BC -
SI-910AH
SI-910A
NaOH-soluble portion of SI-910A
of turf from the primary mound
Organic matter 2mm size from
turf of primary mound
5995 +
185
4675 +
110
SI-910AH is significantly
too old (T=75.2;
T(5%) =11.1; ν=5);
without this, 4515 +
52
(T=5.8; T(5%) =9.5;
ν=4)
5330-4450 cal BC
3370-3020 cal BC
-
-
SI-910B Organic matter 1-2mm size from
turf of primary mound
4315 +
110 -
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Redating Silbury Hill in its monumental landscape
Table 1. (Contd.).
Calibrated date Posterior density
Laboratory Radiocarbon range (95%) estimate (probability)
number Material and context age (BP) δ13C() Weighted mean (BP) confidence (see Figure 4)
SI-910C Organic matter 0.5-1mm size from
turf of primary mound
4570 +
120 -
SI-910CH NaOH-soluble portion of SI-910C 4465 +
130 -
SI-910D Organic matter under 0.5mm size
from turf of primary mound
4530 +
110 -
OxA-11663 Sample 6A (SILB3), dried mosses
(see Table 2) from surface of a
turf from the primary mound
(acid wash only)
3295 +
60 28.1 (T=38.2; T(5%) =3.8;
ν=1)
1740-1430 cal BC -
OxA-11647 Sample 6B (SILB5), dried mosses
(see Table 2) from surface of a
turf from the primary mound
(acid wash only)
3746 +
40 30.4 2290-2040 cal BC -
OxA-14640 Sample 6 (TS1b), dried mosses (see
Table 2) from surface of a turf
from the primary mound
(NaOH-soluble fraction)
3735 +
50 28.9 3634 +
21 (T=7.0;
T(5%) =7.8; ν=3)
2120-1935 cal BC -
GrA-28555 Sample 6 (TS1a), replicate of
OxA-14640 (NaOH-soluble
fraction)
3710 +
80 29.9
OxA-14642 Sample 7 (TS2b), dried mosses (see
Table 2), from surface of a turf
from the primary mound
(NaOH-soluble fraction)
3612 +
31 28.
GrA-28467 Sample 7 (TS2a), replicate of
OxA-1642 (NaOH-soluble
fraction)
3585 +
40 29.9
OxA-14641 Sample 6 (TS1b), dried mosses (see
Table 2) from surface of a turf
from the primary mound (NaOH
and HCl-insoluble fraction)
3898 +
31 28.1 3848 +
17 (T=6.4;
T(5%) =7.8; ν=3)
2560-2205 cal BC 2460-2415 cal BC
(11%) or 2410-
2275 cal BC
(84%)
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Alex Bayliss, Fachtna McAvoy & Alasdair Whittle
Table 1. (Contd.).
Calibrated date Posterior density
Laboratory Radiocarbon range (95%) estimate (probability)
number Material and context age (BP) δ13C() Weighted mean (BP) confidence (see Figure 4)
GrA-28465 Sample 6 (TS1a), replicate of
OxA-14641 (NaOH- and
HCl-insoluble fraction)
3770 +
40 28.9
OxA-14643 Sample 7 (TS2b), dried mosses (see
Table 2), from surface of a turf
from the primary mound (NaOH
and HCl-insoluble fraction)
3848 +
31 27.8
GrA-28466 Sample 7 (TS2a), replicate of
OxA-14643 (NaOH and
HCl-insoluble fraction)
3840 +
40 28.9
Chalk mound
OxA-13210* Sample 1, antler tine, probably red
deer. Not precisely located, but
from early part of tunnel
excavation in April 1968 and
recorded as ‘e.side of chalk block
wall’; There are chalk block walls
around rings 11-13/14 on both
sides of the tunnel (Whittle 1997:
Figures 10-11) about 14-18 m
into the mound, in the makeup
of the chalk mound, and the
sample should belong here
3401 +
36 22.1 3396 +
27 (T=0.0;
T(5%) =3.8; ν=1)
1750-1620 cal BC -
GrA-27336 Sample 1, replicate of OxA-13210 3390 +
40 23.7
OxA-11970 Sample 2, red deer antler, from
clean chalk material above floor
of tunnel at ring 12 on west side
of tunnel, in the outer part of the
mound (Whittle 1997: Figures
10-11)
3634 +
30 23.3 3633 +
25 (T=0.0;
T(5%) =3.8; ν=1)
2125-1920 cal BC 2135-2085 cal BC
(18%) or 2045-
1935 (77%)
GrA-27335 Sample 2, replicate of OxA-11970 3630 +
45 23.7
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Redating Silbury Hill in its monumental landscape
Table 1. (Contd.).
Calibrated date Posterior density
Laboratory Radiocarbon range (95%) estimate (probability)
number Material and context age (BP) δ13C() Weighted mean (BP) confidence (see Figure 4)
GrA-27331 Sample 661-200100864, red deer
antler, from context 30, large
chalk blocks, approximately 2m
below the top of the mound, seen
in the sides of the hole recorded
in 2001
3655 +
45 23.2 2200-1890 cal BC 2195-2170 cal BC
(2%) or 2145-
1930 cal BC
(93%)
I-2795 A mixture of antler fragments from
the 1867 and 1922 cuttings on
the east mound side
2750 +
100 - - -
Chalk walling at top of mound
OxA-13328Sample 661-851, red deer antler,
from context 7, the outer face of a
very substantial chalk wall,
approximately 70 cm below the
top of the mound in Trench B of
excavations in 2001
3856 +
39 22.6 3870 +
24 (T=0.2;
T(5%) =3.8; ν=1)
2465-2210 cal BC -
OxA-14118 Sample 661-851, replicate of
OxA-13328
3878 +
31 22.5
South ditch
BM-841 Red deer antler, from near the
excavated base (not more
precisely recorded) of the south
ditch cutting of 1969 (Whittle
1997: Figure 23). The cutting
reached to within 1m of the base
of the ditch.
3752 +
50 2300-2020 cal BC 2290-2030 cal BC
(95%)
BM-842 Red deer antler, as BM-841 3849 +
43 2470-2140 cal BC 2350-2130 cal BC
(95%)
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Alex Bayliss, Fachtna McAvoy & Alasdair Whittle
(SI-910AH) with the series. As a whole, however, these results are significantly earlier than
the date on the plant material from a similar context provided by Isotopes Inc. (I-4136; see
above).
Finally, two samples each consisting of a single antler recovered from the lowest excavated
part of the south ditch cutting of 1969, were dated at the British Museum in the early 1970s
(Burleigh et al. 1976). Collagen was extracted from these samples and dated as described by
Barker et al. (1971). Probing suggested that the base of the ditch was about 1m below the
base of the trench, so these results should be reasonably close in date to the digging of the
quarry.
These dates from the ditch (BM-841-2) fall rather later than that from the vegetable
material from the turves of the primary mound (I-4136). These results provided the basis
for the estimate of a construction date somewhere between 2800/2500-2400/2000 BC
suggested by Whittle (1997a: 26).
Changed circumstances: the new dating programme
Concluding the report on previous research on Silbury Hill, one of us noted the roughly
70-year intervals at which fieldwork had taken place up to the end of the twentieth century,
but also claimed that ‘it is hard to envisage that future researchers will resist the challenge of
the unanswered aspects of Silbury Hill’, including specifically its dating (Whittle 1997a: 167).
That wish was granted much sooner than expected, and in far from ideal conditions, when
part of the top of the mound collapsed in 2000, because of settling of the fill of previous
tunnels. That led to remedial works, accompanied by further investigations and recording
of the constituents of the mound in 2001 (Chadburn et al. 2005). That work provided
some of the samples reported here. It was also the spur for further survey of, and research
on, the mound (Field 2005; Harding et al. 2005; McAvoy 2005). Further remedial work on
the tunnels will take place in due course to ensure they are properly backfilled, and repair
work will be accompanied by an appropriate level of further archaeological investigation. It
is likely that the repair will involve the re-opening of the Atkinson tunnel of 1968-9 and
the Merewether tunnel of 1849, both of which are blocked at the entrance but not properly
backfilled along their length (Amanda Chadburn, English Heritage, pers. comm., 27 March
2006).
Meanwhile, the new work at the top of the mound provided the spur for a reassessment
of the unsatisfactory existing dating and led to our acquiring a few more samples from the
archive of the Atkinson work assembled in the course of the 1997 publication. This was
further extended by the late John Evans, who provided samples from the buried soil under
the primary mound, which he had collected on his own initiative, for reference purposes,
during the 1968-9 excavations. This helped to broaden the new dating programme.
Objectives
Further dating of the development of Silbury Hill was undertaken in response to the
circumstances of 2000-2001, which highlighted the limitations of the existing dating, and
35
Redating Silbury Hill in its monumental landscape
to contribute to one of the research priorities identified in the archaeological research
agenda for the Avebury World Heritage Site (AAHRG 2001). The availability of AMS and
methodological advances which have been made in the interpretation of radiocarbon dates
over the past decade or so provided the means to produce a rather more robust chronology
for this monument (Bayliss & Bronk Ramsey 2004). This was also the opportunity to
compare the dating of the monumental mound with other constructions in its local area
(summarised in AAHRG 2001; Pollard & Reynolds 2002; Gillings & Pollard 2004) and
beyond, for example at and around Stonehenge (Cleal et al. 1995: 511-35; Bayliss et al.
1997; Bronk Ramsey & Bayliss 2000).
Specifically, the new dating programme was designed to address the following
objectives:
rto date the constructional stages of the mound
rand thereby to be able to compare the development of the mound with other Late
Neolithic constructions in the Avebury area and beyond.
Sampling
The sampling programme was severely restricted by the circumstances of previous
excavations of the monument. Rather little material survives in the archives, and contextual
information is frequently not available or is imperfect. We have sampled as much reliably
contexted material as we could locate. Our programme has concentrated on the archive of
the 1968-70 excavations held in the Alexander Keiller Museum, Avebury, and on material
recovered and excavated in 2000-2001. The archives from all previous work have not been
located, although it should be noted that Richard Atkinson had access in the late 1960s to
at least some material from the 1922 excavations.
Two scraps of animal bone were located from the old land surface under the primary
mound (samples 4 & 5, Table 1). Three blocks of turf were found from the primary mound.
These had been recovered at the time of the excavations of 1968-9 by John Evans and kept
by him; their primary context is confirmed by the calcareous nature of the attached soil
(Cornwall et al. 1997: 28). Dried mosses were picked from the surface of these turves, to
form six bulk samples for AMS dating (Table 1). The identification of the species of moss
in each sample is given in Table 2. In effect, these are replicate samples, and also replicate
the earlier sample (I-4136) from an equivalent context. Multiple chemical fractions were
dated from these samples. Three samples of red deer antler (one from the side of the crater
at the top of the mound caused by the 2000 collapse) have been dated from contexts which
appear to form the makeup of the chalk mound. One further sample of red deer antler was
found in the recent excavations next to what may have been substantial chalk walling very
near the top of the mound, presumably indicating that this sample is later than those from
the main body of the chalk mound.
Because of the difficulties of removing contamination from samples from the mound (see
below), and the technical problem identified with the bone preparation method used in the
Oxford Laboratory when the samples were initially processed (Bronk Ramsey et al. 2004a),
all but one of the new samples have been measured in replicate.
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Alex Bayliss, Fachtna McAvoy & Alasdair Whittle
Table 2. Identification of mosses.
Sample number Laboratory numbers Mosses identified
Sample 6A (SILB3) OxA-11663 Mainly Rhytidiadelphus squarrosus (Hedw.)
Warnst., with some Calliergon cuspidatum
(Hedw.) Kindb., cf. Plagiomnium sp(p), and
some moss indet (mainly leafless or otherwise
eroded shoots)
Sample 6B (SILB5) OxA-11647 Mainly Calliergon cuspidatum (Hedw.) Kindb.,
with some moss indet (mainly leafless or
otherwise eroded shoots)
Sample 6 (TS1) OxA-14640, GrA-28555,
OxA-14641, GrA-28465
Mainly Rhytidiadelphus squarrosus (Hedw.)
Warnst., with some cf. Eurynchium sp(p),
Neckara complanata (Hedw.) H¨
ub.,
Pseudoscleropodium purum (Hedw.) Fleisch, cf.
Plagiomnium sp(p), and some moss indet
(mainly leafless or otherwise eroded shoots)
Sample 7 (TS2) OxA-14642, GrA-28467,
OxA-14643, GrA-28466
Mainly Rhytidiadelphus squarrosus (Hedw.)
Warnst., with some Calliergon cuspidatum
(Hedw.) Kindb., cf. Plagiomnium sp(p), and
some moss indet (mainly leafless or otherwise
eroded shoots)
Results
Thirty radiocarbon results are now available from Silbury Hill (Table 1). They are
conventional radiocarbon ages (Stuiver & Polach 1977). The calibrated date ranges in Table 1
have been calculated using the maximum intercept method (Stuiver & Reimer 1986) and
provide a simple summary of the radiocarbon date of each sample; all other distributions are
based on the probability method (Stuiver & Reimer 1993). All results have been calibrated
using OxCal (v3.10) (Bronk Ramsey 1995; 1998; 2001) and data from Reimer et al. (2004).
Nineteen new measurements were made between 2001 and 2005. Eight of these results
were produced by the Centre for Isotope Research, Rijksuniversiteit Groningen, in 2005.
These samples were prepared and dated as described by Aerts-Bijma et al. (1997; 2001)
and van der Plicht et al. (2000). The other eleven results were produced by the Oxford
Radiocarbon Accelerator Unit between 2001 and 2005. The six samples of dried moss were
processed according to methods outlined in Hedges et al. (1989). The five samples of bone
and antler were initially processed using the gelatinisation protocol described by Bronk
Ramsey et al. (2000). Following the discovery in the laboratory of a contamination problem
associated with this method, in four cases the contaminated material was re-processed,
graphitised, and dated, as described by Bronk Ramsey et al. (2004a). These results are
denoted by an asterisk in Table 1. One of these samples, 661-851, was dated for a second
time using collagen extraction (Law & Hedges 1989; Hedges et al. 1989), followed by the
revised gelatinisation and filtration protocol described by Bronk Ramsey et al. (2004a). The
two measurements (OxA-13328 and OxA-14118) are statistically consistent (Table 1; Ward
& Wilson 1978), as are the pairs of measurements on the two samples where dates from
Oxford on re-filtered material have been replicated by Groningen (samples 1 & 5; Table 1).
37
Redating Silbury Hill in its monumental landscape
This consistency gives us further confidence in the effectiveness of the re-purification process
applied to these samples (see also Bayliss et al. 2007a: Figure 26). Sample 2 was also processed
according to the method described by Bronk Ramsey et al. (2000) at Oxford, but does not
seem to have been affected by the contamination problem, as this result (OxA-11970) is
also statistically consistent with a replicate from Groningen. All these samples were dated by
AMS as outlined in Bronk Ramsey et al. (2004b), except for OxA-11647 and OxA-11663 (a
carbon dioxide target) which were dated as described by Bronk Ramsey and Hedges (1997).
The ten new radiocarbon results from samples of mosses retrieved from the surfaces
of turves incorporated in the primary mound are statistically significantly different, from
each other (T=129.3; T(5%) =16.9; ν=9), from the series of results from bulk organic
soil fractions measured by the Smithsonian Institution in the 1960s (excluding SI-910AH)
(T=365.1; T(5%) =23.7; ν=14), and from the sample of plant material dated from
a similar context in 1968 (T=143.3; T(5%) =18.3; ν=10). The bulk soil samples
probably contained organic matter dating from the whole period of the soil’s formation.
The consistency of the results of the different particle size fractions suggests that these
measurements are probably reliable estimates of the radiocarbon content of this material,
although the resultant date only provides a terminus post quem for the mound. The wide
variation in the new measurements appears to relate to contamination by a younger humic
component in the samples. The four measurements on the acid/base insoluble fraction of
this material are statistically consistent (Table 1) and are considered to be the most reliable for
determining the age of the mosses. Since this material was growing on the surface of the turf,
all the fragments of moss must have grown in the few years before the mound was raised. The
results on the alkali-soluble (‘humic fraction’) are also statistically consistent but are signi-
ficantly younger (Table 1). Since humics can be mobilised and remobilised within sediments,
particularly in an alkaline environment such as the chalk mound of Silbury, it is likely that
these results relate to later contaminants. The varying results on OxA-11663 and OxA-
11647 also seem to relate to the incomplete removal of a younger humic component, as
these samples were fragile and light and so were only treated with acid. For these samples, this
appears to have been insufficient to remove all contaminants. The four new results on the
acid/alkali insoluble fraction of the moss are, however, significantly later than that of the bulk
sample of equivalent material previously dated (I-4136; T=13.2; T(5%) =9.5; ν=4). As
this sample consisted of unburnt plant material from within the turves of the primary mound,
rather than from their surface, the incorporation of some slightly earlier material preserved
in the turf is perhaps not unexpected. For these reasons the four measurements on the acid/
alkali insoluble fraction of the moss have been incorporated in the models presented below.
Interpretation
The new programme for dating Silbury Hill was conceived from the outset within a
Bayesian statistical framework. This allows the chronology of the monument to be formally
estimated, using an explicit statistical methodology, from both the radiocarbon dates and the
stratigraphic sequence revealed by archaeological excavation. This approach was introduced
for the construction of archaeological chronologies more than a decade ago (Buck et al.
1991; 1992; 1994a-c; Bronk Ramsey 1995; Buck et al. 1996), and the impact of its
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Alex Bayliss, Fachtna McAvoy & Alasdair Whittle
routine application is beginning to become apparent (Bayliss & Bronk Ramsey 2004;
Whittle et al. 2007). Since this approach integrates more than one type of information,
it provides date estimates that are not only formal but also more robust and precise than
those reliant on only one element of the chronological information available about a site
(i.e. either the stratigraphy or the radiocarbon dating). To distinguish them from simple
calibrated radiocarbon dates, ranges derived from chronological modelling are printed
in italics in this paper, following emerging convention, along with the relevant parameter
name (often the laboratory number). Such chronologies are interpretative and, particularly
for sites such as Silbury Hill, where analysis of the archaeological record is not unambi-
guous, it can be essential to explore alternative readings (Bayliss et al. 2007a).
The chronological model which incorporates the recorded stratigraphic sequence of all
these samples is infinitely improbable. The most dramatic disconformity is between sample
4 (OxA-13211) and its recorded position as being from the old land surface beneath the
primary mound. This date is at least a millennium later than the replicated samples of
moss fragments from the turves forming the primary mound: from the stratigraphy an
unimpeachably later context. The survival of uncharred mosses and grasses on the surface
of these turves strongly indicates that the mound cannot be of Late Bronze Age date, as
such material would not survive in aerobic conditions for an entire millennium. There
is no obvious explanation for this result, but it is just possible that younger material was
inadvertently introduced (on the soles of footwear for example) into the centre of the mound
either during the eighteenth-century vertical tunnel or the nineteenth-century horizontal
tunnel, or in the subsequent individual and unauthorised explorations of the collapsing
1849 tunnel after 1915, as recorded in correspondence with Richard Atkinson (Whittle
1997a: 10), or indeed during the 1968-9 excavations. An alternative is that the very small
sample in question had been mis-recorded during the excavations.
Sample 661-851, adjacent to the chalk walling very near the top of the mound, recovered
in the recent excavations, also has poor agreement with its apparent stratigraphic position
on top of, i.e. later than, the antler samples from within the makeup of the chalk mound.
In this case, either this sample is redeposited from an earlier context or the dated samples
from the chalk mound do not relate to its primary construction but to later episodes of
modification. In more detail, sample 661-851 was found at the interface of the ‘outer face
of a possible chalk ‘wall’ (7) and a chalk layer (11). Sample 661-200100864 is from a layer
of chalk (30) that is similar in appearance to layer 11, but lower in the uppermost part of
the mound. These layers were found in separate parts of the summit and their stratigraphic
relationship is therefore not strictly known. Sample 2 came from the outer part of the chalk
mound at ring 12 of the 1968-9 tunnel (Whittle 1997a). This is from the outer body of
Silbury III, but perhaps sufficiently close to its sloping outer face to conceivably represent
latermodicationorslippage.
Model 1
A chronological model for the development of Silbury Hill is shown in Figure 4. This model
incorporates the interpretation that sample 661-851 (Wal l ; Figure 4) is redeposited, and
so the construction of the chalk mound is best dated by the antlers recovered within it.
39
Redating Silbury Hill in its monumental landscape
Figure 4. Probability distributions of dates from Silbury Hill. Each distribution represents the relative probability that an
event occurs at a particular time. For each of the dates, two distributions have been plotted: one in outline, which is the
result of simple radiocarbon calibration, and a solid one, based on the chronological model used (in this case model 1); the
‘event’ associated with, for example, GrA-27331, is the growth of the dated antler. Distributions other than those relating to
particular samples correspond to aspects of the model. For example, the distribution ‘construct Silbury I’ is the estimated date
when the primary turf mound was raised. Measurements followed by a question mark have been excluded from the model for
reasons explained in the text, and are simple calibrated dates (Stuiver & Reimer 1993). The large square brackets down the
left-hand side along with the OxCal keywords define the overall model exactly.
Sample 1 has been excluded from the model on the grounds that its location within the
outer chalk mound was not precisely located, that it is statistically significantly later than the
other two samples from the chalk mound, and that it may therefore relate to later, peripheral
modification of the mound. Consequently, we think that samples 2 and 661-200100864
(sample 2 and GrA-27331; Figure 4) may provide a more reliable indication of the date of
the chalk mound. This is reinforced by the dates obtained on antlers from near the base
of the south ditch cutting of 1969 (BM-841-2; Figure 4), since the chalk from this quarry
must presumably have gone into the formation of the mound. The two south ditch dates are
statistically significantly different to those from the chalk mound (T=21.2; T(5%) =7.8;
ν=3) and so we further suggest that these samples may provide a terminus ante quem for
the initiation of the chalk mound as a whole.
This reading of the archaeological sequence formalised in model 1 allows us to estimate
that the primary mound of Silbury Hill was raised in 2415-2190 cal BC (95% probability;
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Alex Bayliss, Fachtna McAvoy & Alasdair Whittle
Figure 5. Probability distributions of dates from Silbury Hill, based on model 2. The format is identical to that for
Figure 4. The large square brackets down the left-hand side along with the OxCal keywords define the overall model exactly.
Figure 6. Probability distributions showing the number of calendar years taken to construct Silbury Hill. These distributions
are derived from the models shown in Figures 4 and 5.
construct Silbury I ;Figure4),or2335-2235 cal BC (68% probability). The chalk mound was
constructed in 2125-2075 cal BC (11% probability)or2055-1915 cal BC (84% probability;
construct Silbury II-III;Figure4),or2035-1950 cal BC (68% probability). It should be
noted that both of the dated antler samples from the chalk mound come from its outer or
uppermost parts – in Atkinson’s terms from Silbury III. It is possible therefore that the antlers
from the south ditch cutting, which are earlier, may relate to the episode of construction
which in Atkinsons terms formed Silbury II.
By comparing the estimates for the construction of Silbury I and what we have argued
is an estimate for the construction of Silbury III in model 1, we can suggest that the
Silbury Hill mound was a phased development, taking 140-435 years (95% probability;
build Silbury (Model 1);Figure6),or220-365 years (68% probability) to reach its near-final
41
Redating Silbury Hill in its monumental landscape
form. On the basis of the date of sample 1, further modification of the outermost parts
of the mound is indicated as lasting into the early second millennium cal BC (sample 1;
Figure 4).
Model 2
An alternative reading of this sequence is shown in the chronological model defined in
Figure 5. In this case, all four antler samples from the chalk mound are considered to relate
to later modifications of the outer and uppermost parts of Silbury III, and the antler sample
from the chalk walling at the top of the mound (661-851; Wall ; Figure 5) is interpreted
as a tool relating to topping out the chalk mound. This early construction of the chalk
phase of the mound conforms with the dates of the antlers from the south ditch cutting
(BM-841-842; Figure 5), given that chalk from that ditch contributed to the make-up of
the chalk mound.
Model 2 suggests that the primary mound was constructed in 2445-2265 cal BC
(95% probability;construct Silbury I ;Figure5),or2390-2295 cal BC (68% probability).
Silbury III was topped out in 2405-2270 cal BC (79% probability)or2260-2205 cal BC
(16% probability;Wal l ; Figure 5). By taking the difference between these two estimates,
it can be suggested that the principal building phase of Silbury Hill took between 1-
115 years (95% probability;build Silbury (Model 2);Figure6),or1-50 years (68%
probability).
Although this estimate is more in line with previous interpretations of a shorter rather
than longer building process (Atkinson 1968; 1970; 1978; Whittle 1997a: 26), we feel that
this is the less plausible of the two models. This is because of the consistently late dates from
antlers recovered from the chalk mound. I-2795 was made on bulk material from at least two
areas of excavation on the eastern flank of the mound, and so may easily contain material of
a range of ages. It is more difficult to dismiss samples 1 and 2 as later. The precise location
of sample 1 is uncertain and so might relate to later modifications, but sample 2 is securely
located (see above, and Table 1), some metres within the outer part of the chalk mound.
It is even more difficult to overlook the result from 661-200100864 (GrA-27331). This
antler is from the recent excavation of 2001, securely located in a deposit of chalk blocks
2m from the top of the mound, apparently below the level from which sample 661-851 was
recovered.
We would like to stress that neither of the models for the chronology of Silbury Hill
presented here is entirely satisfactory. We prefer model 1 because it requires less special
pleading than model 2. This programme has, however, substantially advanced our knowledge
of the chronology of the monument. Both models agree in placing the raising of the primary
mound in the twenty-fourth or twenty-third century cal BC (Figure 7). On the basis of the
antler samples from the south ditch cutting, they agree in suggesting that at least some part
of the chalk mound was raised shortly after. The interpretations differ as to whether the
monument reached its near-final form at this time or whether there was a major phase of
enlargement (Silbury III) in the years around 2000 cal BC (construct Silbury II-III ;Figure7).
Under either reading, further modifications around the margins of the mound continued
well into the Bronze Age.
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Alex Bayliss, Fachtna McAvoy & Alasdair Whittle
Figure 7. Probability distributions of key dates from Silbury Hill, derived from model 1 (Figure 4) and model 2 (Figure 5).
The format is identical to that for Figure 4.
Discussion: the world recreated
Social explanations have tended to dominate interpretive discussion of Silbury Hill, but the
great monumental undertaking was both a social fact and an expression of cosmology and
worldview. How do the chronological models presented here change our views of the heroic
enterprises of the Late Neolithic of southern Britain?
Previous estimates of the time it may have taken to construct Silbury Hill were strongly
influenced by the absence of visible hiatus in the form of turflines reflecting periods of
standstill; recent remedial work appears to have confirmed their absence. Richard Atkinson
favoured a quick build, perhaps over a decade or so (1968; 1970; 1978), while Whittle
suggested a slightly more extended process of ‘one or more generations’ (1997a: 26). Our
preferred model 1 now suggests a significantly longer span over which building took place
(build Silbury (Model 1);Figure6).
These estimates, especially those of model 1, have important implications for how we
view the sociality of the building process. Previously, one temptation (classically in Renfrew
1973) has been to see major earthwork and related enterprises as the expression of chiefdom
society: concentrated programmes under the influence of dominant figures able to exercise
their authority and influence, if not power, to mobilise labour over finite periods of time.
If the building process, however, took in this case rather longer – and we can refer also to
extended chronologies for both Avebury (Pollard & Cleal 2004) and Stonehenge (Cleal et al.
1995: 511-35; Bayliss et al. 1997) – how does that view stand up? We cannot dismiss the idea
of centralised authority on the basis of a longer timescale alone, since that is quite compatible
with more concentrated episodes of political activity within it. Perhaps all monuments of
any scale may have involved considerable discussion and contestation (Richards 2005). The
goal of extending and perhaps eventually completing a major place of devotion, pilgrimage
43
Redating Silbury Hill in its monumental landscape
and labour could have been a focus for the activities, claims and propaganda of putative
chiefs or other leaders over several generations. And we can summon other new evidence for
the possibility, if not likelihood, of dominant social personae at this time, seen for example
in the recent discovery of the probably broadly contemporary Beaker-associated ‘Amesbury
Archer’ near Stonehenge (Fitzpatrick 2002).
On the other hand, an extended timescale for construction seems rather to throw the
enterprise into a more fluid social setting. Arguments and contestation surrounding the
construction process as envisaged by Richards (2005) suggest a lack of clearly established
leadership. Dominant figures may have emerged, and by the end of the long and perhaps
episodic process (see Barrett 1994: 163) of deciding to build, mobilising the labour of the
wider community, energising subsequent generations after short-term lapses, and directing
the great works as they rose higher and higher and nearer to the limits of what was possible
in that particular form. Another account stressed the likely importance of charismatic
individuals (Whittle 1997a: 147-9), and the timescales offered here may suggest that it was
a succession of these, within a more widely shared agreement through the moral community
about the necessity and desirability of the massive undertaking, who kept the project going
for so long.
It is not possible to keep the social, conceptual and spiritual dimensions of the
monumental mound apart. The possibility of broad general agreement (if regularly contested
in details) about the project through the moral community can be linked to the notion of
ritual cycle: ideas about sacred realms, the past and the beginnings of the world, which led
people to such communal undertakings of prodigious labour investment (Whittle 1997a:
166). One of us has referred to ‘myths of return, and belief in renewal, allied to a desire to
both honour and emulate the ancestors, in a matrix of cyclical, ritual time (Whittle 1997a:
166). This kind of view has been elaborated by Parker Pearson and Ramilisonina (1998:
Figure 8; Parker Pearson 2000) for the Avebury area, but concentrating upon an argued
contrast between the circles of the living in the form of the West Kennet palisade enclosures
and the circles of the ancestors in the form of Avebury.
Both these models have been constructed on the basis of very imprecise chronology,
and assume that all the major monuments of the Avebury area were built and in use at
more or less the same time (Whittle 1997a: 164-5; Parker Pearson & Ramilisonina 1998:
Figure 8). Parker Pearson (2000: Figures 17.4-5) gives a more diachronic view, in which
Avebury is built before 2500 cal BC and is then joined by the West Kennet palisade
enclosures and Silbury Hill between 2500 and 2000 cal BC. Imperfect though the preferred
model 1 presented here may be, it serves to begin to refine the picture further, especially
when combined with other advances in our understanding of the third millennium cal
BC chronology for the region. The long barrows and causewayed enclosures of the region
were already very old, potentially of ancestral status (Whittle 1997a: Figure 87), which we
can now estimate to belong to specific centuries of the fourth millennium cal BC. That
is another story, to be presented elsewhere (Whittle et al. 2007). The ditches of Windmill
Hill were still infilling in the twenty-fourth and twenty-third centuries cal BC, and Beaker
pottery there could belong to that sort of date or later (Whittle et al. 1999). The secondary
filling of the chambers and passage of the West Kennet long barrow was probably completed
around or soon after c.2400 cal BC (Bayliss et al. 2007b). The small, short-lived enclosure
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Alex Bayliss, Fachtna McAvoy & Alasdair Whittle
Figure 8. Probability distributions of dates from the stone settings at Stonehenge, incorporating the interpretation of the
sequence proposed by Cleal et al. (1995: Appendix 3). The format is identical to that for Figure 4. The overall model is that
described by Bronk Ramsey and Bayliss (2000), with the model for phase 3 defined by the large square brackets down the
left-hand side along with the OxCal keywords.
at Beckhampton appears to date to the mid-third millennium cal BC or before, with
Grooved Ware at the base of the ditch and dates variously given as between 2650/2500
and 2510/2300 cal BC (Gillings et al. 2002: 255) or for construction between 2900 and
2600 cal BC (Pollard & Cleal 2004: 125). The initial, slight earthwork at Avebury was
followed by the major ditch and bank construction perhaps in the second quarter of the
third millennium cal BC (Pollard & Cleal 2004); the construction or completion
of the Outer Stone Circle, however, may have taken rather longer (Pitts & Whittle 1992).
The West Kennet palisade enclosures are not precisely dated, but can be assigned to the
second half of the third millennium cal BC (Whittle 1997a: Table 1). We do not have
45
Redating Silbury Hill in its monumental landscape
radiocarbon dates for the West Kennet or Beckhampton Avenues, nor for The Sanctuary
(Pollard & Cleal 2004: 125).
So there remain many uncertainties, but it looks increasingly unlikely that the
construction phases of all these monuments fall in exactly the same horizon. The situations
envisaged by both Whittle (1997a: Figure 87) and Pearson and Ramilisonina (1998: Figure
8; note again Parker Pearson 2000), with a number of monuments in contemporary and
inter-linked use, may only have come into being after long histories of development. The
same point can of course be made for Stonehenge itself (Cleal et al. 1995; Bayliss et al.
1997). By the time of the twenty-fourth or twenty-third centuries cal BC, when we suggest
that the construction of Silbury Hill may have begun, the sarsen settings had probably been
set up, but the bluestone circle and horseshoe had probably not, perhaps being raised at the
end of the third millennium cal BC. (Unfortunately, the archives for earlier work at both
Silbury Hill and Stonehenge are probably now insufficient to get any more precision for this
comparison.)
The published model for the dating of Stonehenge (Cleal et al. 1995: Appendix 3;
Bayliss et al. 1997; Bronk Ramsey & Bayliss 2000) has been recalculated using the updated
internationally agreed calibration data of Reimer et al. (2004), and is shown in Figure 8. This
model treats each major setting as a unitary construction, and so stratigraphic relationships
between one element of a setting can be taken as representative of the whole. On this basis,
the sarsen trilithons must be earlier than the bluestone settings, and the sarsen circle must
be earlier than the Y and Z Holes (Cleal et al. 1995, Figure 268). Our revised estimates for
the construction of the stone settings at Stonehenge are shown in Table 3. We have also,
however, remodelled the dating of Stonehenge in Figure 9, using the practical suggestion of
Humphrey Case (1997: 263-5) that the trilithons can only have been constructed before the
construction of the sarsen circle, simply because there could scarcely have been space to put
them up within an already standing sarsen circle. In this reading, UB-3821 from the sarsen
circle (on an antler from the stonehole of Sarsen 1) is interpreted as residual. The estimates
for the construction of the major stone settings of Stonehenge derived from this model are
also shown in Table 3.
Our alternative chronologies for Silbury Hill and the stone settings at Stonehenge are
shown in Figure 10. This demonstrates that, according to model 1 for Silbury Hill, it is
probable that the great mound was constructed after the major sarsen settings of Stonehenge,
but before the bluestone settings. If model 2 is preferred, however, the sequence is more
dependent on our interpretation of the data from Stonehenge. If Cases reading is followed,
then both Silbury I and the sarsen settings of Stonehenge may fall in the twenty-fourth
century cal BC. If, however, the already published model is preferred, then the sarsens
may have reached Stonehenge and been set up there from the twenty-sixth century cal BC
onwards. We find Case’s logistical argument attractive, if the stone settings were unitary
constructions. This may be supported by the presence of a Beaker sherd in the stonehole of
Trilithon 54 (Cleal et al. 1995: 198). As yet another variation, we could see the settings as the
outcome of longer and more piecemeal construction – thus not unitary or quick building
events. In that case, sarsen circle and trilithons could have been begun from the same
point onwards, to be dated by UB-3821 and OxA-4840 (from Trilithon 53/54) respectively,
and been completed by the dates given by OxA-4839 (Trilithon 57) and BM-46 (claimed
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Alex Bayliss, Fachtna McAvoy & Alasdair Whittle
Figure 9. Probability distributions of dates from the stone settings at Stonehenge, incorporating the revised interpretation of
the sequence proposed by Case (1997: 263-5). The format is identical to that for Figure 4. The overall model is that described
by Bronk Ramsey and Bayliss (2000), with the revised reading for phase 3 defined by the large square brackets down the
left-hand side along with the OxCal keywords.
erection ramp for Trilithon 56). In this scenario, Silbury Hill is either later than the sarsen
settings at Stonehenge or was constructed as they were nearing their final form. In our view,
multiple readings of the chronologies of both these monuments are currently possible, and
it is a matter of archaeological interpretation to determine which are preferred. Without
further excavation, it is unlikely that we can reach a consensus on these issues.
If, despite the difficulties at both Silbury Hill and Stonehenge, a more robust sequence is
beginning to emerge, so too is a stronger sense of change with passing generations. There
may have been layered senses of time at work here, some looking back to ancestral pasts,
already referred to above in the notion of ritual cycle. But this notion may itself have been in
47
Redating Silbury Hill in its monumental landscape
Table 3. Posterior density estimates for the construction of the stone settings at Stonehenge, according to the alternative models for phase 3 of the
monument shown in Figures 8 and 9.
Figure 8 (after Cleal et al. 1995) Figure 9 (after Case 1997)
95% Probability 68% Probability 95% Probability 68% Probability
Parameter (unless otherwise noted) (unless otherwise noted) (unless otherwise noted) (unless otherwise noted)
Sarsen Circle 2580-2470 cal BC 2575-2560 cal BC (14%) or
2535-2490 cal BC (54%)
--
Sarsen Trilithons 2455-2215 cal BC 2405-2265 cal BC 2455-2210 cal BC 2405-2265 cal BC
Bluestone Circle 2280-2245 cal BC (6%) or
2235-2030 cal BC (89%)
2205-2125 cal BC (45%) or
2090-2040 cal BC (23%)
2275-2245 cal BC (3%) or
2240-2025 cal BC (92%)
2200-2125 cal BC (45%)
or 2090-2045 cal BC
(23%)
Bluestone Horseshoe 2280-2250 cal BC (2%) or
2210-1925 cal BC (93%)
2195-2175 cal BC (8%) or
2145-2015 cal BC (57%)
or 1995-1980 cal BC (4%)
2275-2250 cal BC (1%) or
2210-1925 cal BC (94%)
2195-2170 cal BC (7%) or
2145-2020 cal BC (58%)
or 1995-1980 (3%)
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Alex Bayliss, Fachtna McAvoy & Alasdair Whittle
Figure 10. Probability distributions of key dates from Silbury Hill, derived from model 1 (Figure 4) and model 2 (Figure
5) and of key dates from Stonehenge (see Bronk Ramsey & Bayliss 2000 and Figures 8 and 9). Estimates for the overall
prevalence of Beakers in Scotland are derived from Sheridan (forthcoming: Table 1), and those of Beakers in England from
Needham (2005: Tables 1-7). The format is identical to that for Figure 4.
part a creation of its own times. There is a mixture of old and new. Monuments continued to
be built in places which had seen monument construction already over centuries, and people
were attracted to the same loci for the placement of Beaker graves. The circular earthworks,
and avenues, can be argued to continue – with variation and innovation – older traditions
of enclosure going back into the fourth millennium cal BC. But there is much that can be
identified as novel around the twenty-fourth or twenty-third centuries cal BC. It is probable
that the major sarsen settings of Stonehenge began before the initiation of Silbury Hill
(Figure 10), suggesting that the latter could have been some kind of response from people
to the north, with their trajectories of development converging a little further into their
49
Redating Silbury Hill in its monumental landscape
respective histories at the end of the third millennium cal BC. Both Stonehenge and Silbury
Hill are novel in their different ways, the idea of existing timber settings being transformed
into stepped stone versions at Stonehenge (judging by the profile of the completed sarsen
settings: Whittle 1997b), and the concept of the circular mound, already known in other
monuments and on an impressive scale in the passage graves of the Boyne, being magnified
in the feats of Silbury Hill: both perhaps in their different ways acting as symbols of cosmic
origin or rebirth (Whittle 1997a; 1997b). Each may have played off the other, as novel,
grandiose conceptions of how the world came into being, promoted and developed in the
changing circumstances of the times.
Around this time another way of thinking and acting as social beings may have begun to
come into existence through the Beaker network, in part a shared ideology consistent enough
with communal traditions but in part a way of emphasising chosen individuals and events in
the mortuary process. We have modelled data given by Needham (2005) for English Beakers
to suggest beginnings in 2475-2315 cal BC (95% probability; start English Beakers; Fig-
ure 10) or 2425-2350 cal BC (68% probability); and data given by Sheridan (forthcoming)
for Scottish Beakers to suggest beginnings in 2385-2235 cal BC (95% probability; start
Scottish Beakers; Figure 10) or 2345-2270 cal BC (68% probability). This dating may refer
principally to the placement of Beakers in graves, and it remains an open question for the
present whether Beakers were in use in other contexts slightly before these dates. In either
case, we can now see the aggrandisement of both Stonehenge and Silbury Hill in close
relation to the appearance of novel material culture and practices.
It has been commonplace for some time to contrast older if not archaic ways of doing
things and of thinking about the world with new practices associated with the Beaker
network. One version of that found expression in the contrast between ‘ritual authority
structures’ and ‘prestige goods economies’ (Thorpe & Richards 1984), and the separation
of Grooved Ware and Beakers in our Late Neolithic chronologies (e.g. Cleal & McSween
1999) might seem to reinforce that kind of distinction. But the chronological model offered
here for Silbury Hill, datings for other monuments including Avebury and Stonehenge,
and revised Beaker chronologies, serve now to complicate that kind of scenario. Those were
complex times (Figure 10), and the rising mass of Silbury Hill as much as the silhouette
of the sarsen settings at Stonehenge may now symbolise the many dimensions of that
history.
The future
We hope that we have stressed enough that while the preferred chronological model presented
here helps to clarify sequences in the third millennium cal BC and has many implications,
it is not yet nearly robust enough for a monument of the importance of Silbury Hill.
The potential of the existing archive for providing more precise results has probably been
exhausted. Silbury Hill needs a better chronology still, and the further mitigation work on
the tunnels will provide an opportunity to collect a fresh series of precisely contexted samples
for radiocarbon dating. To misquote Jacquetta Hawkes on Stonehenge, every Silbury Hill
should get the generations it deserves.
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Acknowledgements
We are grateful to the late John Evans for his interest and provision of samples; Polydora Baker for animal
bone identifications; Matt Canti for soil analysis; Allan Hall of York University for identification of mosses; and
Amanda Chadburn for encouragement and advice. We thank the staff of the Oxford Radiocarbon Accelerator
Unit and the Centre of Isotope Research, Rijksuniversiteit Groningen, for dating the new samples. Figure 1b
was prepared by John Vallender. Stuart Needham, Alison Sheridan, Mike Parker Pearson, Amanda Chadburn,
Frances Healy and two anonymous Antiquity referees gave invaluable information and constructive criticism of
earlier drafts.
References
Aerts-Bijma, A.T., H.A.J. Meijer &J. van der
Plicht. 1997. AMS sample handling in
Groningen. Nuclear Instruments and Methods in
Physics Research B 123: 221-25.
Aerts-Bijma, A.T., J. van der Plicht &H.A.J.
Meijer. 2001. Automatic AMS sample combustion
and CO2collection. Radiocarbon 43: 293-98.
Avebury Archaeological and Historical Research Group
2001. Archaeological research agenda for the Avebury
World Heritage Site. Salisbury: Wessex Archaeology.
Atkinson, R.J.C. 1967. Silbury Hill. Antiquity 41:
259-62.
–1968. Silbury Hill, 1968. Antiquity 42: 299.
–1969. The date of Silbury Hill. Antiquity 43: 216.
–1970. Silbury Hill, 1969-70. Antiquity 44: 313-4.
–1978. Silbury Hill, in R. Sutcliffe (ed.) Chronicle:
essays from ten years of television archaeology: 159-73.
London: British Broadcasting Corporation.
Barker, H., R. Burleigh &N. Meeks. 1971. British
Museum natural radiocarbon measurements VII.
Radiocarbon 13: 157-88.
Barrett, J.C. 1994. Fragments from antiquity: an
archaeology of social life in Britain, 2900-1200 BC.
Oxford: Blackwell.
Bayliss, A. &C. Bronk Ramsey. 2004. Pragmatic
Bayesians: a decade integrating radiocarbon dates
into chronological models, in C.E. Buck & A.R.
Millard (ed.) Tools for constructing chronologies: tools
for crossing disciplinary boundaries: 25-41. London:
Springer.
Bayliss, A., C. Bronk Ramsey &F.G. McCormac.
1997. Dating Stonehenge, in B. Cunliffe & C.
Renfrew (ed.) Science and Stonehenge: 39-59.
Oxford: British Academy.
Bayliss, A., C. Bronk Ramsey, J. van der Plicht &
A. Whittle. 2007a. Bradshaw and Bayes: towards
a timetable for the Neolithic. Cambridge
Archaeological Journal 17(1), Supplement, 1-28.
Bayliss, A., Whittle, A. &Wysocki, M. 2007b.
Talking about my generation: the date of the West
Kennet long barrow. Cambridge Archaeological
Journal 17(1), Supplement, 85-101.
Bronk Ramsey, C. 1995. Radiocarbon calibration and
analysis of stratigraphy. Radiocarbon 36: 425-30.
–1998. Probability and dating. Radiocarbon 40: 461-74.
–2001. Development of the radiocarbon calibration
program. Radiocarbon 43: 355-63.
Bronk Ramsey, C. &A. Bayliss. 2000. Dating
Stonehenge, in K. Lockyer, T.J.T. Sly & V.
Mihˇ
ailescu-Bˆ
ırliba (ed.) CAA96: computer
applications and quantitative methods in archaeology:
29-39. Oxford: British Archaeological Reports.
Bronk Ramsey, C. &R.E.M. Hedges. 1997. A gas ion
source for radiocarbon dating, Nuclear Instruments
and Methods in Physics Research B 29: 45-9.
Bronk Ramsey, C., T. Higham, A. Bowles &
R.E.M. Hedges. 2004a. Improvements to the
pre-treatment of bone at Oxford. Radiocarbon 46:
155-63.
Bronk Ramsey, C., T. Higham &P. Leach. 2004b.
Towards high precision AMS: progress and
limitations. Radiocarbon 46: 17-24.
Bronk Ramsey, C., P.B. Pettitt, R.E.M. Hedges,
G.W.L. Hodgins &D.C. Owen. 2000.
Radiocarbon dates from the Oxford AMS system:
Archaeometry datelist 30. Archaeometry 42: 459-79.
Buck, C.E., W.G. Cavanagh &C.D. Litton. 1996.
Bayesian approach to interpreting archaeological data.
Chichester: Wiley.
Buck, C.E., J.A. Christen, J.B. Kenworthy &C.D.
Litton. 1994a. Estimating the duration of
archaeological activity using 14C determinations.
Oxford Journal of Archaeology 13: 229-40.
Buck, C.E., C.D. Litton &E.M. Scott. 1994b.
Making the most of radiocarbon dating: some
statistical considerations. Antiquity 68: 252-63.
Buck, C.E., C.D. Litton &S.J. Shennan. 1994c. A
case study in combining radiocarbon and
archaeological information: the early Bronze Age
settlement of St. Veit-Klinglberg, Land Salzburg,
Austria. Germania 72: 427-47.
Buck, C.E., J.B. Kenworthy, C.D. Litton &A.F.M.
Smith. 1991. Combining archaeological and
radiocarbon information: a Bayesian approach to
calibration. Antiquity 65: 808-21.
51
Redating Silbury Hill in its monumental landscape
Buck, C.E., C.D. Litton &A.F.M. Smith. 1992.
Calibration of radiocarbon results pertaining to
related archaeological events. Journal of
Archaeological Science 19: 497-512.
Buckley, J.D., M.A. Trautman &E.H. Willis. 1968.
Isotopes radiocarbon measurements VI.
Radiocarbon 10: 246-94.
Burleigh, R., A. Hewson &N. Meeks. 1976. British
Museum natural radiocarbon measurements VIII.
Radiocarbon 18: 16-42.
Case, H. 1997. Stonehenge revisited. Wiltshire
Archaeological and Natural History Magazine 90:
161-8.
Chadburn, A., F. McAvoy &G. Campbell. 2005.
Inside the hill. British Archaeology 80
(January/February 2005): 14-15.
Cleal, R.M.J. &A. McSween. (ed.) 1999. Grooved
Ware in Britain and Ireland. Oxford: Oxbow.
Cleal, R.M.J., R. Montague &K.E. Walker. 1995.
Stonehenge in its landscape: twentieth-century
excavations. London: English Heritage.
Cornwall, I., G.W. Dimbleby &J.G. Evans. 1997.
Soils, in A. Whittle (ed.) Sacred mound, holy rings.
Silbury Hill and the West Kennet palisade enclosures:
a Later Neolithic complex in north Wiltshire: 26-9.
Oxford: Oxbow.
Field, D. 2005. Surface story. British Archaeology 80
(January/February 2005): 15-8.
Fitzpatrick, A. 2002. ‘The Amesbury Archer’: a well
furnished Early Bronze Age burial in southern
England. Antiquity 76: 629-30.
Garwood, P. 1991. Ritual tradition and the
reconstitution of society, in P. Garwood, D.
Jennings, R. Skeates & J. Toms (ed.) Sacred and
profane: 10-32. Oxford: Oxford University
Committee for Archaeology.
Gillings, M. &J. Pollard. 2004. Avebur y. London:
Duckworth.
Gillings, M., J. Pollard &D. Wheatley. 2002.
Excavations at the Beckhampton enclosure, Avenue
and Cove, Avebury: an interim report on the 2000
season. Wiltshire Archaeological and Natural History
Magazine 95: 249-58.
Harding, R., A. Chadburn, F. McAvoy &G.
Campbell. 2005. The future. British Archaeology
80 (January/February 2005): 18-9.
Hedges, R.E.M., C.R. Bronk &R.A. Housley. 1989.
The Oxford Accelerator Mass Spectrometry facility:
technical developments in routine dating.
Archaeometry 31: 99-113.
Law, I.A. &R.E.M. Hedges. 1989. A semi-automated
pretreatment system and the pretreatment of older
and contaminated samples. Radiocarbon 31:
247-53.
McAvoy, F. 2005. Silbury Hill, Wiltshire. An assessment
of the conservation risks and possible responses arising
from antiquarian and archaeological investigations
deep into the Hill. Fort Cumberland, Portsmouth:
English Heritage Research and Standards
Department unpublished report.
Needham, S.P. 2005. Transforming Beaker culture in
north-west Europe: processes of fusion and fission.
Proceedings of the Prehistoric Society 71: 171-218.
Parker Pearson, M. &Ramilisonina. 1998.
Stonehenge for the ancestors: the stones pass on the
message. Antiquity 72: 308-26.
Parker Pearson, M. 2000. Ancestors, bones and
stones in Neolithic and Early Bronze Age Britain
and Ireland, in A. Ritchie (ed.) Neolithic Orkney in
its European context: 203-14. Cambridge:
McDonald Institute for Archaeological research.
Pitts, M. &A. Whittle. 1992. The development and
date of Avebury. Proceedings of the Prehistoric Society
58: 203-12.
Pollard, J. &J. Cleal. 2004. Dating Avebury, in R.
Cleal & J. Pollard (ed.) Monuments and material
culture. Papers in honour of an Avebury archaeologist:
Isobel Smith: 120-9. East Knoyle: Hobnob Press.
Pollard, J. &A. Reynolds. 2002. Avebur y: the
biography of a landscape.Stroud:Tempus.
Reimer, P.J., M.G.L. Baillie, E. Bard, A. Bayliss,
J.W. Beck, C.J.H. Bertrand, P.G. Blackwell,
C.E. Buck, G.S. Burr, K.B. Cutler, P.E. Damon,
R.L. Edwards, R.G. Fairbanks, M. Friedrich,
T.P. Guilderson, A.G. Hogg, K.A. Hughen, B.
Kromer, F.G. McCormac, S. Manning, C.
Bronk Ramsey, R.W. Reimer, S. Remmele, J.R.
Southon, M. Stuiver, S. Talamo, F.W. Taylor,
J. van der Plicht &C.E. Weyhenmeyer. 2004.
IntCal04 Terrestrial Radiocarbon Age Calibration,
0-26 cal kyr BP. Radiocarbon 46: 1029-58.
Renfrew, C. 1973. Monuments, mobilisation and
social organisation in Neolithic Wessex. in C.
Renfrew (ed.) The explanation of culture change:
539-58. London: Duckworth.
Richards, C. 2005. A choreography of construction:
monuments, mobilization and social organization
in Neolithic Orkney, in J. Cherry, C. Scarre & S.
Shennan (ed.) Explaining social change: studies in
honour of Colin Renfrew: 103-13. Cambridge:
McDonald Institute for Archaeological Research.
Sheridan, A. forthcoming. Scottish Beaker
chronology: an assessment of the currently-available
radiocarbon dating evidence, in J. Turek & M.
Krutova (ed.) Beaker days in Bohemia and Moravia.
Prague: Archaeologica.
Sigalove, J.J. &A. Long. 1964. Smithsonian
Institution radiocarbon measurements I.
Radiocarbon 6: 182-8.
52
Research
Alex Bayliss, Fachtna McAvoy & Alasdair Whittle
Stuckenrath, R. &J.E. Mielke. 1973. Smithsonian
Institution radiocarbon measurements VIII.
Radiocarbon 15: 388-424.
Stuiver, M. &H.A. Polach. 1977. Reporting of 14C
data. Radiocarbon 19: 355-63.
Stuiver, M. &P.J. Reimer. 1986. A computer
program for radiocarbon age calculation.
Radiocarbon 28: 1022-30.
–1993. Extended 14C data base and revised CALIB 3.0
14C age calibration program. Radiocarbon 35:
215-30.
Thorpe, I.J. &C. Richards. 1984. The decline of
ritual authority and the introduction of Beakers
into Britain, in R. Bradley & J. Gardiner (ed.)
Neolithic studies: a review of some current research:
67-84. Oxford: British Archaeological Reports.
Trautman, M.A. &E.H. Willis. 1966. Isotopes, Inc.
radiocarbon measurements V. Radiocarbon 8:
161-203.
van der Plicht, J., S. Wijma, A.T. Aerts, M.H.
Pertuisot &H.A.J. Meijer. 2000. Status report:
the Groningen AMS facility. Nuclear Instruments
and Methods in Physics Research B 172: 58-65.
Wainwright, G. 1989. The henge monuments.
London: Thames & Hudson.
Walton, A., M. Trautman &J.P. Friend. 1961.
Isotopes, Inc. radiocarbon measurements I.
Radiocarbon 3: 47-59.
Ward, G.K. &S.R. Wilson. 1978. Procedures for
comparing and combining radiocarbon age
determinations: a critique. Archaeometry 20:
19-31.
Whittle, A. 1997a. Sacred mound, holy rings. Silbury
Hill and the West Kennet palisade enclosures: a Later
Neolithic complex in north Wiltshire.Oxford:
Oxbow.
–1997b. Remembered and imagined belongings:
Stonehenge in its traditions and structures of
meaning, in B. Cunliffe & C. Renfrew (ed.)
Science and Stonehenge: 145-66. London: British
Academy.
Whittle, A., A. Barclay, A. Bayliss, L. McFadyen,
R. Schulting &M. Wysocki. 2007. Building for
the dead: events, processes and changing
worldviews from the 38th to the 34th centuries cal
BC in southern Britain. Cambridge Archaeological
Journal 17(1), Supplement, 123-47.
Whittle, A., J. Pollard &C. Grigson. 1999. The
harmony of symbols: the Windmill Hill causewayed
enclosure, Wiltshire. Oxford: Oxbow.
53
... A series of trenches were also cut through two palisade enclosures at West Kennet (Whittle 1997). This campaign of new excavation was accompanied by research into the archives of previous investigations, particularly the publication and subsequent dating of Richard Atkinson's excavation on and within Silbury Hill in 1968-70 (Bayliss et al. 2007a;Whittle 1997) and a reassessment of the date and development of Avebury itself (Pitts and Whittle 1992). The subsequent decades have seen continued work in the Avebury region, given focus by the Archaeological Research Agenda for the Avebury World Heritage site (AAHRG 2001). ...
... The alternative model published by Bayliss et al (2007b;fig 9), incorporating the sequence (Fig 19) proposed by Case (1997) with the antler (UB-3821) from the Sarsen Circle excluded as being residual, has also been re-run. This is based on the simple architectural logic that the Sarsen Trilithons must have been erected before the Sarsen Circle (Case 1997). ...
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... Clearly, this area and period witnessed mound building (as well as the construction of other monument types) on a scale unknown before or after and it is interesting to note that this highly intensive activity, which also includes the first major phase of stone settings at Stonehenge (Darvill et al. in press), coincided with the arrival of the earliest English Beakers (papers in Allen et al. 2012;Fitzpatrick 2011). Whilst there is much we do not understand about the introduction of the 'Beaker package' to Britain, as previously suggested (Bayliss et al. 2007; papers in Allen et al. 2012) it seems beyond coincidence that the occurrence of these truly colossal and largely novel monuments with the introduction of new materials, new people and new lifeways are related, perhaps as an assertion of power in the face of innovation. ...
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... A monograph is currently in preparation which will set out all these works in full. A full dating programme is also in progress and the results are eagerly awaited; radiocarbon dates processed prior to the work described here and based on archived material as well as an antler fragment recovered from the summit in 2001 suggest that the mound was initially raised in the twenty-fourth or twenty-third century BC with a possible enlargement in the years around 2000 BC (Bayliss et al. 2007). ...
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