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At the Heart of the African Acheulean: Kilombe 1
Photo ©JAJ Gowlett
At the Heart of the African Acheulean
Gowlett, J.A.J., Brink, J.S., Herries, A.I.R., Hoare, S., Onjala, I and Rucina, S.M. 2015. At the heart of
the African Acheulean: the physical, social and cognitive landscapes of Kilombe.
In Settlement, Society and Cognition in human evolution: Landscapes in Mind (editors F.Coward,
R.Hosfield and F. Wenban-Smith. Cambridge, Cambridge University Press, pp. 75-93.
ISBN 978-1-107-02688-9
Authors’ Preprint
At the Heart of the African Acheulean: Kilombe 2
AT THE HEART OF THE AFRICAN ACHEULEAN: THE PHYSICAL,
SOCIAL AND COGNITIVE LANDSCAPES OF KILOMBE
John A.J. Gowlett, Department of Archaeology, Classics and Egyptology, University
of Liverpool L69 3GS, UK
James S. Brink, Florisbad Quaternary Research, National Museum, P.O Box 266,
Bloemfontein, 9300, South Africa and Centre for Environmental Management,
University of the Free State, South Africa
Andy I.R. Herries, Australian Archaeomagnetism Laboratory, Archaeology Program,
School of Historical and European Studies, Faculty of Humanities and Social Sciences,
La Trobe University, Melbourne, 3086, VIC, Australia, and Geomagnetism Laboratory,
School of Environmental Sciences, University of Liverpool, L69 7ZE, UK.
Sally Hoare, ACE, Department of Archaeology, Classics and Egyptology, University
of Liverpool L69 3GS, UK
Isaya Onjala, National Museums of Kenya, P.O. Box 40658, Nairobi, Kenya
Stephen M. Rucina, National Museums of Kenya, P.O. Box 40658, Nairobi, Kenya
At the Heart of the African Acheulean: Kilombe 3
ABSTRACT
Kilombe is known as an extensive late Lower Pleistocene Acheulean site complex in the Rift
Valley in Kenya. We report here on recent research which has explored a longer
stratigraphic succession around the sites, casting light on landscape development and
occupation through much of the last million years. With its position near the Equator the site
complex is close to the geographic and chronological heart of the Acheulean, and ideally
suited to investigations, because of the extent of preservation of ancient landscape, and the
potential for dating and recovery of environmental information
The new surveys have concentrated on studying the site area in its local setting near the foot
of Kilombe volcano, which became extinct in the early Pleistocene, and formerly held a crater
lake, currently under investigation. In 2011, bifaces were also found at the mouth of the
volcano gorge. Events on the Acheulean main site terminated with a volcanic eruption which
deposited the 3-banded tuff (3BT), now dated to ca. 990,000 years, but the sequence
continues above this level, and is capped locally by an ashflow tuff (AFT) some 7 metres
thick, the product of a landscape-transforming eruption probably deriving from an ancestor
of the present day Menengai. To the east and west, the sequence then resumes with major
exposures of tuffaceous sediments belonging to the Middle and Upper Pleistocene, and
containing Middle Stone Age and Later Stone Age artefacts. These provide the chance to
study newer landscapes within the same catchment.
The Kilombe main site permits very rare opportunities to compare large numbers of bifaces
and other artefacts which are of the same age across a distance of around 200 metres, and so
build up a picture of local variability within a site complex. The site area allows comparisons
– within the complex to explore its structure of variation, on a regional scale of site
catchment, and then externally to help evaluate issues across the greater Acheulean world
and through the Middle Stone Age. Although the development of the MSA can be seen only
sketchily at present, the preservation of both contexts and artefacts demonstrates the potential
to elaborate a longer record.
At the Heart of the African Acheulean: Kilombe 4
INTRODUCTION: THE KILOMBE SITES AND THEIR PLACE IN THE
ACHEULEAN
Kilombe is one of a series of great Acheulean site complexes in eastern Africa. In this
paper we use new evidence to reflect on the ways in which studies of its landscapes –
geographical, ecological and sociocultural - have developed through a generation of
studies. The first research in the 1970s was already influenced by a multi-
disciplinary world – in East Africa, the geologists set ‘frameworks’ (Bishop 1972,
1978), and archaeologists worked to place their finds in stratigraphic, chronological
and taphonomic contexts (Isaac 1977). The social lives of early humans were already
a preoccupation (e.g. Washburn and DeVore 1961), and their use of large landscapes
was already recognized. Even so, things have changed, and the social has moved to
the centre. When Clive Gamble wrote in 1979 that the emphasis had shifted, to
‘resource exploitation, demography, settlement location, interaction and mating
networks’ (1979:35), he was setting out an aspiration - one that is even now hard to
realize for the Palaeolithic. At Kilombe, the old model of technology is familiar, but
the opportunities of new approaches are conspicuously available.
Our renewed research since 2008 has aimed to develop a much fuller picture of
Kilombe’s various landscapes and their chronology. Not only are the opportunities
on the ground vastly improved compared with a generation ago, but also there is a
framework of social, cognitive, ecological and comparative studies which makes it
far more feasible to develop a much broader picture. Our ability to date such sites
has also improved in the last 30 odd years with improved instrumentation, a better
understanding of regional faunal evolution and in some cases entirely new
geochronological methods at our disposal.
The Kilombe background
The Acheulean site complex at Kilombe was found by the geologist W.B. Jones in
1972. Its exploration was first taken up by W.W. Bishop (1978) and one of the
authors (Gowlett 1978), leading onto the new research which we discuss. The sites
lie on the western flank of the Kenya Rift Valley (Fig. 1), about 6 km south of the
Equator, and 40 km NW of Nakuru. In this area there are no visible major rift faults.
Instead the landscape is dominated by the Plio- Pleistocene Rift volcanoes of
Londiani (ca 3010 m), and Kilombe (ca 2380 m), which sits at the side of Londiani
extending further towards the Rift Valley floor (Fig 2, Fig. 3). The main lines of
drainage are the Molo and Rongai rivers, which rise on the Mau escarpment about 50
km to the SW, and flow past Kilombe northward towards Lake Baringo, some 100
km away. Essentially this is a relatively old landscape – last lava flows at Kilombe
have been dated to between 2.05-1.65 Ma (Jones 1975), and Kilombe volcano was
probably already extinct before one and a half million years ago (we discuss below a
lake that formed in the crater). There has been relatively little later faulting; and the
depth of river valleys indicates their considerable age. At its southern end the
Baringo basin is marked by the Menengai volcano, around 30 km SE of the Kilombe
At the Heart of the African Acheulean: Kilombe 5
sites, and visible from these localities. Menengai took shape about 200,000 years ago
in its current form and was transformed again by a recent massive caldera explosion
near the end of the Pleistocene (Leat 1984). It is probably the descendant of earlier
active Pleistocene volcanoes (Jones 1985), and responsible for much of the deposition
of pyroclastics in the area (Jones and Lippard 1979).
STRATIGRAPHY AND LOCALITIES
The original research at Kilombe concentrated largely on the main Acheulean site,
which seemed exciting enough, with its extraordinary density of bifaces. At the time
there was very limited time to move beyond Kilombe Main Site, although other
small biface occurrences were found in the area. In dense bush it was a struggle to
map the various outcrops and archaeological occurrences with theodolite, plane table
and old air photograph cover. Now the regional perspective can be developed much
more easily and fully through the (recent) ready availability of high-resolution
satellite imagery.
The Kilombe Main Site (GqJh1) still provides one of the best local stratigraphies in
the region. It was initially described by Bishop (1978) in an account which has
largely stood the test of time, but which recent work has modified. The chief
challenge was to understand a major break in the sequence, where a thick ashflow
tuff was deposited over the landscape.
The lower sequence and Main Site
At the base is trachyphonolite lava, dated to 1.70 ± 0.05 Ma (1.75-1.65 Ma) (Jones and
Lippard 1979). This lava is extensive in the area, forming a low ridge stretching
outwards from the base of the volcano towards the Molo river. Across the area it
crops out at intervals, generally mantled to a depth of several metres by reddish-
brown and brown clays which are its weathering products. The trachyphonolite
formed an irregular surface, and its ridges appear to have constrained drainage,
probably directing stream channels, and helping to cause some local ponding. The
trachytes of Kilombe volcano and Londiani abut the trachyphonolite to the north.
Although the stratigraphic relationship is not known, a K-Ar date on a trachyte flow
of 1.90 ± 0.15 Ma (2.05-1.75 Ma) suggests that the two are potentiallyco-eval,
especially given uncertainties in these older ages. The ‘brown clays’ of Bishop (1978),
immediately overlying the trachyphonolite in the Main Site area, can actually be
subdivided in three zones, a lower reddish-brown clay (RBC), overlain by a
yellowish tuff (YT) that occurs in localized areas and an upper dark brown clay
(DBC) (Figure 5). Fossils occur mainly at or near the contact between the two clays,
which may represent an old landsurface onto which the yellowish tuff was
deposited. A small amount of fauna came from the ‘Brown Clays’ of Main Site in the
1970s (Bishop, 1978). Recent excavations recovered more fauna that came almost
entirely from this old landsurface at or near the contact between the lower RBC and
upper DBC. The fauna includes elephant, hippo and bovids (see below). The top of
At the Heart of the African Acheulean: Kilombe 6
the clays marks another major break, and coincides on the main site with the main
artefact horizon, with its many bifaces. This is our first archaeological landscape.
This stratigraphy can be traced across several kilometers, but the Main Site (GqJh1)
stands out because of the presence of a broad shallow depression, lower by about
one metre than the adjacent surfaces of the DBC. This depression must signal a local
erosional event, following which the very large numbers of bifaces were deposited.
Eventually the depression filled in with pale weathered tuffaceous material, which
contains a few abraded artefacts, presumably washed in from the margins. This pale
pumiceous tuff (PPT) seals in the hand-axe layer throughout the Main site.
Hominins were still present: a further artefact horizon occurs in a lightly developed
palaeosol at the top of PPT, about a metre above the main horizon. Although it
remains well within Acheulean time, only flakes and flake tools have been found
(Gowlett 1978).
The 3-banded tuff complex
The next key event was a series of volcanic eruptions which blanketed the whole area
with the 3-banded lapilli tuff (3BT), named for its distinctive profile, and traceable
across several kilometers as an important marker horizon. This was a landscape-
changing event. Bishop (1978) interpreted it as a primary airfall through standing
water, and it appeared to map out a ponded area perhaps 2km across. We can now
trace it in an area extending approximately three by two kilometers, but its levels
vary so considerably that the old explanation of a lake is no longer tenable. Rather,
the tuff seems to have blanketed the catchment of small streams which ran off the
eastern side of the ridge of trachyphonolite lavas, which projects south from Kilombe
mountain. Levels of the tuff can be seen to decline steeply from west to east, through
as much as 100 metres. The gradient is steeper than that found in the Molo river,
which runs on a parallel course less than 2 km further south, and so cannot result
from faulting, although minor faults may have occurred. These findings suggest the
steep headwaters of local streams, which probably joined the Molo (or proto-Molo)
within a few kilometers downstream. These local streams ran across an irregular
surface of trachyphonolite lavas, coated with the clays which formed from their
weathering. Recent erosion has re-exposed some of the channels which ran across
the trachyphonolite surface.
The 3BT is somewhat degraded in parts of its westerly exposures, perhaps indicating
erosion at its margins. In places, particularly to the east, its bands are slightly more
separated, suggesting some significant difference in age between the eruptions,
rather than the few hours that might have been envisaged. Dagley et al. (1978)
showed in one of the first palaeomagnetic studies applied to the Acheulean that the
3BT recorded a reversed polarity, demonstrating an age older than the Brunhes-
Matuyama boundary. This suggests the 3BT and Acheulean layers beneath it are
older than 780,000 years based on the new dates for this boundary. Dagley et al.
(1978) expressed caution in the interpretation of the results because the three samples
taken were highly magnetized, possibly owing to a lightning strike. New
At the Heart of the African Acheulean: Kilombe 7
palaeomagnetic sampling confirms the presence of reversed polarity throughout the
3BT in more than one location that argues against the strong remanence being a
lightning strike. A single layer within the 3BT also recorded a normal polarity that
may represent a short geomagnetic excursion, which would argue against the 3BT
being a short even, however, more detailed sampling is needed to confirm the
presence of such an event. In contrast the clay layers (RBC, DBC) below the hand-axe
layer record normal polarity. Based on the fauna from the site, which shows affinities
with Olduvai Gorge Bed III-IV (see below), this normal polarity period is correlated
to the Jaramillo Sub-Chron between 1.07 and 0.99 Ma (Herries et al. 2011; in prep.).
As such, fauna can be dated to between 1.07 and 0.99 Ma, with the hand-axe layer
dating more broadly to sometime between 1.07 and 0.78 Ma. PPT records reversed
polarity towards its top and mixed polarity towards its base, which may suggest that
the hand-axe layer dates close to the reversal at the end of the Jaramillo SubChron
at~990,000 years old (Herries et al. 2011; in prep.). Further work is still needed to
identify the exact locations of the various polarity reversals within the sequence and
constrain the ages of all the archaeological and fossil layers. The landscape of the late
Lower Pleistocene is completed by new knowledge of a lake which occupied the
Kilombe crater and is also older than 780,000 years based on a reversed polarity (and
is under study by SH) (see below).
Farmhouse Cliff and the ashflow tuff (AFT)
Recent investigations have confirmed that hominins were still present in the new
landscapes overlying the 3BT. The sediments consist of a sequence of red-brown
weathered pumiceous tuffs some 15 m thick (the Farmhouse cliff, and lateral
equivalents), with sparse occurrences of hand-axes at widely separated points. Most
significant is the discovery in 2010 of a small biface site at GqJh3-West, with
sufficient specimens to allow comparisons. These deposits are capped by an ashflow
tuff some 7 m thick, a major feature of the landscape which Jones (1975; Jones and
Lippard 1979) refers to the Lower Menengai tuffs (dated by K-Ar to ca. 0.3 Ma). The
ashflow tuff (AFT) indicates a major series of Middle Pleistocene eruptions which
must have transformed the whole landscape. The Acheulean was still extant just
before these major eruptions, as confirmed by a biface found in 2009 around one
meter below the ashflow tuff, about 1500 m NE of the main exposures.
The ashflow tuff (AFT) forms a prominent feature in the modern landscape, usually
marking the top of cliffs along the southern edges of the Kilombe exposures (Bishop
1978), and also capping a scarp facing west towards Moricho.Jones and Lippard
(1979) recognized the AFT as a Middle Pleistocene feature dated to a Menengai
eruption at ca 300,000. Although Leat (1984) believed that the AFT can be linked
with a more recent Menengai eruption (ca 30,000 ka), our work has confirmed an
older age, as argued by Jones (1985). The AFT is widespread in the area north of the
Molo river, and can be traced all the way from the side of the Molo river up to the
top of the Kilombe Farmhouse cliff (Fig.4, Fig.5). It thus mantled a landscape in
At the Heart of the African Acheulean: Kilombe 8
which the Molo river valley already existed. In high areas of topography overlying
sediments have vanished, and the ashflow tuff itself has been eroded and in places
breached, but elsewhere other sediments overlie it, indicating a long timescale of
events consistent with Middle Pleistocene age.
The later sediments
A further suite of impressive sediments representing the Middle and Upper
Pleistocene, extends widely along the southern flanks of Kilombe volcano, but was
virtually unexplored until our recent research. Some 30 metres thick, in places they
have been eroded to form natural amphitheatres and huge gullies (Jennings 1971). In
the sequence these sediments appear to be younger than the ashflow tuff. The AFT
largely caps the trachyphonolite ridge which extends south from Kilombe Mountain,
but in the areas to the west and to the east, it occurs at lower topographic levels, and
appears to be blanketed by the later sediments. The extensive deposits consist of red
sediments and further tuffs, visible especially in spectacular exposures at Moricho
about 2 km west of Kilombe, and in huge gullies to the southeast of the mountain,
towards the Rift Valley floor. These exposures, 20 to 30 metres thick, include content
of Middle Stone Age (MSA) and Later Stone Age (LSA) artefacts, mainly but not
entirely made of obsidian. Typical long MSA points have been found in several
areas, suggesting broad age limits of 50,000 – 250,000 years. Some are made of
obsidian, others of fine-grained lava. In places there is also a microlithic component.
Most of the red sediments have a characteristic layer cake appearance, with
alternations of paler tuffs and earthy sediments. At Moricho artefacts have been
located low down in the sequence, just a few metres above the lowest tuffs. In the
Kilombe catchment area (the Acheulean sites), this same series is represented by
channels of streams which descended from high levels, cutting the older sediments.
The channels are often floored with brown tuffaceous grits, and sometimes include
other tuffs in their infilling. They were interpreted by Bishop (1978) as an integral
part of the Farmhouse Cliff suite of pumiceous tuffs which immediately overlies the
three-banded tuff. They are however much later features, postdating the erosional
breach of the ashflow tuff, and containing obsidian artefacts of the MSA.
Fragmentary faunal remains have been found in the base of one such channel in the
GqJh1 main site area. In 2011 a further MSA site was found at the western margin of
Kilombe farm in the direction of Moricho, within one of the channel fills, in and
around a yellowish tuff horizon (site GqJh3-200). It has produced numerous
artefacts including long points. The artefacts are entirely fresh, sometimes with a thin
calcareous coating. The points, made of obsidian, are visibly similar to those from
Porc Epic in Ethiopia (Pleurdeau 2006). Broadly similar material was dated to ca.
130,000 at Nasera and Mumba rockshelters in northern Tanzania (Mehlman 1991).
From surface finds these levels had formerly been thought to belong to the LSA, but
the discovery of typical MSA long points in situ would suggest an age of >50 ka for
almost the entire sequence save superficial deposits. In total, then, the Kilombe
sequence can be seen to preserve numbers of landscapes and sites from at least one
At the Heart of the African Acheulean: Kilombe 9
million years ago up to very recent times.
REFLECTIONS ON THE NEW LANDSCAPES
In the new research since 2008 Kilombe Mountain has come to dominate the picture
even more than it did. The original phase of research was able simply to treat the
Acheulean sites as the key – lakeside - feature of an immediate local landscape, with
just dimmest perceptions of what lay beyond. It was known that some hand-axes
were made of trachyte, probably from Kilombe mountain, and that a very few bifaces
of obsidian came from much further away, so the hand-axes in some way ghosted
out a larger landscape, but in all other respects the research was site-centred by the
constraints of resources. In short, there was a large Acheulean hand-axe site holding
centre stage within a framework chiefly known to geologists. On top was simply a
hint of MSA or LSA activities in the form of scatters of obsidian artefacts.
Now, the basic interpretation shifts from the idea of a lake to a secluded valley by the
foot of the volcano and it can be seen that the Acheulean occurred regularly across
the area, often at low density. It is preserved for us mainly in a valley descending
eastwards from the trachyphonolite ridge (henceforth the Kibberenge valley). The
stream was less than 2km away from the Molo river across the interfluve, but it may
have run for several kilometers or more before finding its confluence with the river.
Although the volcano was already extinct at least 1.5 Ma ago, it had shaped this local
and regional drainage. The rivers Molo and Rongai, draining into the Baringo basin
from the SW pass close by the mountain. The streams radiating from the west, south
and east of the mountain make their way more or less directly into the Molo.
Although the substrate of lavas became blanketed by 50 metres or more of Lower,
Middle and Upper Pleistocene sediments, we can now see that as both faulting and
erosion of hard rocks have been limited, there has been a rare essential continuity in
the landscape which hominins inhabited and exploited.
Several indicators now give us some picture of the local environment around one
million years ago. The fauna comes almost entirely from the contact zone between
the lower (RBC) and upper (DBC) brown clays at the north end of the main site, in
the 4m of sediments underlying the main artifact horizon. As no fauna has been
observed at the same levels elsewhere, its local preservation suggests an area where
the clays accumulated rapidly, but in two or more distinct phases, indicating periods
of erosion or stillstands. Low ridges of trachyphonolite appear to have created a
tendency for very local ponding, probably in a zone not much more than 100 metres
across, as indicated by the shallow depression in the brown clays, and the infilling
with pale material. On the eastern side erosion had cut two (or possibly more)
narrow exit channels in the rock. These may be the key to interpretation, as they
could easily become blocked by vegetation or sediment choking.
Although bones are not prolific, several taxa are now known. Hippopotamus is most
At the Heart of the African Acheulean: Kilombe 10
common, with elephant also present. There is a range of bovids, from giant buffalo
down to gazelle-size. One piece of rodent microfauna has also been preserved.
These remains are entirely consistent with the idea that the immediate environment
was well-watered, and probably swampy in places. The grey-green clays of the main
site may indicate gleying, and sandy runnels show the presence of ephemeral
streams in the site area.
At about the level of the fauna a thin yellowish tuff (YT) occurs, which preserves root
casts indicating the presence of grassy cover.
Further evidence of a well-watered environment comes from the crater lake. The
sediments were first reported by Jennings (1971) although McCall (1964) had been
inclined to see them as a product of caldera formation rather than as lacustrine. We
now know that lake sediments were deposited over a period, preserving thin
laminations and occasional ripple marks through at least 10m depth. They are
overlain by very thick homogeneous tuff, and have reversed magnetic polarity,
indicating an age >780,000 years and most likely <1.78 Ma based on the youngest age
of lava flows from the volcano.
The presence of such water bodies could tally with the idea of Trauth et al. (2005)
that there was a prolonged period of favourable climate in the late Lower
Pleistocene, about a million years ago, and that numerous Acheulean sites are
associated with this. As the idea of a sizeable lake associated with the 3BT can no
longer be sustained, and as the exact age of the crater lake is not yet known, it is
important to withstand any temptation to build such a link by ‘assimilation’. The
key factor in the environment was the presence of high mountains which attract
more rainfall than lower regions in this part of the Rift. Although the later
environments are less known to us, the same topographic factors would operate in
influencing climate.
The ‘langage’ of the artefacts
The French term ‘langage’ allows us to highlight the way in which artefacts can
speak to represent a world beyond themselves, pointing to a network of activities
that for the early Palaeolithic is beyond the reach of any other category of evidence.
The Acheulean: Here clearly the dominant feature remains the extensive artifact
horizon of the Kilombe main site, with hundreds of Acheulean bifaces exposed
across a surface that runs for at least 200 metres in different directions (Gowlett 1978,
1992, 1994, 2005 &c.) (Fig. 5, Fig. 6). Apart from aspects of landscape, the Kilombe
bifaces have offered the basis for various studies of cognitive capabilities, including
the sense of proportion (Gowlett 1984, 2011, especially favoured ratios such as 0.61 or
Golden Section (Boselie 1984)), the role of allometry (Crompton and Gowlett 1993),
and investigations of the presence of traditions (Lycett and Gowlett 2008). In terms
of site formation processes the essential point about Kilombe is that the favoured
At the Heart of the African Acheulean: Kilombe 11
landscape was stable for some considerable time, and then rapidly covered in. Mary
Leakey noted that, like Olduvai Bed I, the site is highly unusual in preserving
artefacts on a clayey (rather than sandy or silty) surface (pers. comm.). The Kilombe
complex thus provides a highly unusual – almost unique - opportunity to look at
local variation within Acheulean bifaces on a single surface (Fig. 6) – a local
landscape (complexes such as the Somme or Boxgrove allow different comparisons
of facies: Tuffreau et al. 1997; Pope et al. 2006). The stable facies shows that people
were attracted by a prolonged conjunction of circumstances, including the presence
nearby of a suitable raw material. This was abundant: the bifaces are chiefly made of
the local trachyphonolite (about 93%). Artefacts are chemically weathered to a pale
grey colour, but when broken through show the original near-black colour of the
rock. It seems that boulders of fresh trachyphonolite were available nearby. They
were knapped to produce large biface-flakes, some of which still preserve the
boulder cortex on their dorsal surfaces, although the boulders themselves hardly
appear on the site.
Almost all the remaining bifaces are made of trachyte, available from the flows of
Kilombe volcano about 3 km away. This rock would not be transported to the main
site area by local streams owing to drainage directions, so its presence indicates a
fairly regular human movement from and to the volcano area. In 2011 two bifaces of
trachyte were found by the mouth of the gorge which emerges on the east side of
Kilombe volcano (Fig. 3), confirming Acheulean presence on the trachyte flows
(although these specimens are undated). Several obsidian bifaces have also been
found on the main site. These must have been carried a much greater distance, but
they are not from the sources used at the Kariandusi sites, 60 km to the South East.
At Gadeb in Ethiopia rare obsidian bifaces were similarly transported a long distance
(Clark 1980).
The number of bifaces discarded across the surface can be calculated very roughly.
In excavations mean densities vary from 4 per sq metre to 2 per sq m. There are
indications that these are typical values over an area of ca. 100 x 50 metres as a
minimum – which would give a value of ca. 5000 sq metres multiplied by 3
(approximately), = 15000. Arguably the total number is less important than the
strong message of repeated return. If bifaces were ‘cheap’ in terms of raw material
and effort and people kept returning to a ‘favoured place’, then even if just one task-
group of six people visited the area three times a year discarding two bifaces each,
that could create a discard of around 100 bifaces per three years, or 1000 per 30 years,
translating to some 10,000 bifaces in 300 years. Although some permutation of such
repeated activity has to be anticipated to explain phenomena such as Kilombe, two
features stand out about the surface:
(1) the general similarity of the bifaces across the area
(2) a contrasting variation of individual parameters, which vary far beyond random
expectation, making the output distinctly characterisable area by area.
This local character suggests that bifaces were ‘related’ in groups of about 20 to 60.
At the Heart of the African Acheulean: Kilombe 12
Cluster analysis has proved helpful for finding most similar bifaces. It is possible, for
example, to consider all the areas, and to determine whether the nearest ‘relative’ to a
biface is found close to it, or some way distant. A study using Wishart’s Density
analysis found that to a considerable extent the most similar bifaces were grouped
together in an area, or in adjacent areas (Gowlett 2005). This evidence hints at small
groups working together on particular occasions, and sometimes the same individual
hand may be involved a number of times (cf Gamble and Porr 2005).
We know the basic procedural parameters of the Acheulean far better than the uses
to which the artefacts were put. Potts et al. (1999) demonstrate that the large biface
concentrations at Olorgesailie are an extremely rare feature on the landscape, hugely
outnumbered by low density artifact occurrences. The same holds true for the
Kilombe area. It should be emphasised that the principal explanation cannot be
taphonomic – at less than two km from their sources, the streams at Kilombe would
have been simply unable to collect and spread out this quantity of material. The two
main competing causes are that these are centres for butchery, or for the exploitation
of plant resources. The first has the difficulty that so many carcases would have to
be brought to one place, the second that no plant resource has been identified that
would lead to so many similar occurrences across such a large part of the Old World.
A third possibility is that these may be working areas where bifaces were finished (or
rejected), and where a variety of tasks took place. At Kilombe, Olorgesailie and
elsewhere consistently small quantities of trimming flakes are found with the bifaces,
indicating minor reworking, but not the principal stages of production.
One issue is whether variation is constrained in a local tradition. The small biface
assemblage recently found above the 3-banded tuff – hence probably several
thousand years younger than the main horizon – offers a valuable test. Does it (KW)
fit within a single distinctive Kilombe tradition? It has similar length range, but
includes unusually narrow or elongate specimens. Similar ones, however, are found
in one small sub-assemblage of the main horizon, AS. Discriminant analysis (DA) is
one means of plotting the Kilombe assemblages against other Acheulean sites (Fig.
8). It underlines the generally distinctive nature of the Kilombe grouping, which
keeps to its own ‘site space’, comfortably including the later KW assemblage, but it
also emphasizes a ‘variable sameness’ of the Acheulean, which allows far distant
assemblages to be similar. Thus the heavyweight KZ strays into the zone of Cornelia
(Brink et al. 2012) and Kalambo Falls Sangoan (B4) (Clark 2001), whereas EL tends
towards the Kalambo Falls Acheulean (A6).
Notably, the Thickness/Breadth ratio varies enormously across the single surface.
Contemporaneous local subassemblages vary from as little as 0.35 to about 0.56 in
mean thickness, with differences significant at the one per cent level. These
differences emphasise that thickness/breadth can never be taken as an index of
chronology, because it is a prime means of adjusting mass. In East Africa it is
hazardous to see it as an index of refinement, but refinement does exist. Symmetry
in bifaces is another issue of broad interest (e.g. Machin et al. 2007; Lycett 2008).
At the Heart of the African Acheulean: Kilombe 13
Contrary to some thinking, hand-axes with an advanced symmetry occur from at
least one million years ago (cf Figure 7). . The patterns suggest that some of the small
departures from symmetry are intentional symmetry-breaking probably linked with
handedness in use.
Finally, Kilombe demonstrates along with other sites that early humans were capable
of leaving a great deal of material on the landscape. Even if the repeated nature of
activity is a part-explanation, we still see hominins ‘at home’ on the landscape, and
the notion that large sites come only with modern humans is not supported by the
very visible evidence.
The Middle and Later Stone Age: The later exposures along the southern flank of
Kilombe volcano contribute to sequence building, offering the opportunity to map
out later landscapes in the same area. They are currently less well known than the
early levels, but have great potential because of the scale of the exposures. The
scatters of MSA and LSA artefacts suggest a steady and widespread human use of
the slopes on the south side of the volcano. At least in part this took place at the side
of stream channels. They also show us clearly a new pattern of resource use,
involving the use of imported raw materials. Some obsidian used in the region came
from the Naivasha area around 100 km away (Merrick and Brown 1984), but there
did remain some use of the local lavas, even for some long MSA points. Even so, the
outline evidence is enough to show that hominins were operating on a new scale of
network. Changes of technology may of course have helped this to operate: the
small blanks of high quality raw material are far more transportable than the earlier
hand-axes.
This shift from the obvious larger tools to their smaller successors, parts of more
sophisticated systems, is something that can be traced with a rare continuity in this
region (McBrearty & Brooks 2000; Basell 2008; Wendorf and Schild 1974), as at
Kapthurin to the north (McBrearty 1999, Johnson & McBrearty 2010; Tryon and
McBrearty 2002, 2006; Tryon 2006) and at Prospect Farm and Olorgesailie to the
south (Michels et al 1983).
Conclusions: a valley by a volcano
The exposures of Kilombe allow us to read a record of an early Pleistocene landscape
at several levels, and to get first insights into equivalent later Middle and Upper
Pleistocene occupations – all tucked away in the same Kibberenge valley.
At the base, the Kilombe main Acheulean complex gives a breadth of view which it
will be hard to match. In the full picture of the early Acheulean record it appears
that such large hand-axe concentrations are an anomaly, unusual on the landscape,
as at Olorgesailie (Potts et al. 1999). Where they do occur, as at Kilombe, on close
inspection they point to the existence of many minor sites and artifact scatters of
At the Heart of the African Acheulean: Kilombe 14
different kinds. These make up a fuller landscape. They occur in different
permutations in different site complexes. The great value of Kilombe for the
Acheulean is that it preserves one huge paene-contemporaneous surface, and so
allows intercomparisons of a kind that are very rarely possible. They show that
variations within a site complex can be as great as those between them.
Nevertheless, there is also a distinctive local Kilombe character, preserved and
transmitted through its various assemblages.
Its artifacts allow particular insights into various practical and cognitive capacities,
perhaps most of all the ability of early humans to carry out transformations of their
material culture, varying the physical scale and form of the bifaces in a highly
controlled way. This ability to transform, to have a sense of proportion, is an
important underpinning for many later cultural developments. A wider perspective
on Kilombe comes from the greater landscape – the outlying exposures, the crater
lake, and the finds of the higher levels. Together these offer a treasure trove of
archaeological possibilities, with the possibility of assembling successive snapshots
of a changing picture.
All together its evidence gives an impression of system and organization in the
hominins who settled there. They repeated similar activities many times, but also
varied them. They had strong rules for their behaviour, but also subtle ones.
Working in from more general frameworks of human evolution and sociality we can
say a good deal about the capacities of these early humans, almost certainly Homo
erectus. Demonstrably they worked in sizeable groups, and conveyed information
across those very accurately. They appear to have been ‘mapped’ to their
environment strongly, in a local tradition. The artefacts and their settings give us
some idea of the strength of communication flows. The ideas of the social brain also
help to give some insight into the capabilities that we should expect (Gamble et al.
2011). They predict the existence of language at least 500,000 years ago (Dunbar
1998), and anatomical evidence points in the same direction. How simple would that
language be, and what could it achieve? We do not know, but the content and
complexity of the Kilombe cultural package measures up with the idea that a large
and detailed body of information was transmitted effectively.
At the Heart of the African Acheulean: Kilombe 15
Acknowledgements
Our thanks are owed to many others, including Derek Roe, the late Bill Bishop, Glynn Isaac and Pat Carter, to
Willy Jones, Laura Basell, Fabienne Marret-Davies, Darren Curnoe, Robin Crompton, Stephen Lycett, Ginette
Warr, Sian Davies, Mimi Hill and Natalie Uomini, as well as to colleagues in the Social Brain project – most
notably Clive Gamble, and Robin Dunbar. JAJG is grateful for support from the British Academy Centenary
Project, AHRC, and help and permissions from the President’s Office and National Museums of Kenya,
especially Emma Mbua. AIRH acknowledges the support of an Australian Research Fellowship linked to ARC
Discovery Grant DP087760 and funding from UNSW Faculty of Medicine. We also thank especially Maura
Butler, and last but most certainly not least Jean-Claude (J.C.) Tubiana, recently departed and much missed.
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At the Heart of the African Acheulean: Kilombe 19
Figures
1. Some important Acheulean and Middle Stone Age (MSA) sites in Africa
At the Heart of the African Acheulean: Kilombe 20
2. The regional context of Kilombe at the south end of the Baringo basin.
At the Heart of the African Acheulean: Kilombe 21
At the Heart of the African Acheulean: Kilombe 22
3. Kilombe – the site region showing the exposures of Kilombe and Moricho in
relation to Kilombe mountain and the Molo valley. The white dotted line indicates
the position of the landscape section shown in Fig. 3a, stretching from the Molo
valley at the SE to the crater lake at the NW.
4. Kilombe – section of landscape and exposures along a line of 6 km from the River
Molo to Kilombe crater (vertical scale x 4 horizontal). The position of the Kilombe
main site is indicated by a box. Note at km 2.5-3 the very different heights of the
ashflow tuff 1.3 km behind the section line and 200m on the observer’s side of it.
The drop of ca. 100m in 1.5 km, which cannot be explained by faulting, results from
the gradient of the valley floor (sloping down towards observer).
At the Heart of the African Acheulean: Kilombe 23
5. General section of Kilombe Main site (modified in the light of recent work after
Bishop 1978, Gowlett 1994). On the main site Middle Stone Age artefacts and
fauna are found in the basal fill of channels which formed following the erosional
breach of the ashflow tuff. Units in stratigraphic sequence:
Channel deposits cutting AFT, and containing MSA artefacts
AFT – ash flow tuff
Farmhouse Cliff – pumiceous tuffs
3-banded tuff
PPT – pale pumiceous tuffs covering artefact horizon
Main Acheulean artefact horizon
Reddish brown clays including fauna
Trachyphonolite lava
At the Heart of the African Acheulean: Kilombe 24
6. Kilombe – A plan of the main site. Note how the mean value of Thickness/Breadth
in bifaces varies markedly from area to area.
At the Heart of the African Acheulean: Kilombe 25
7. Bifaces from Kilombe:(a) A ‘typical’ specimen, close to the Golden Section ratio.
Length 128 mm and Breadth/Length ratio 0.62. (b) A fine specimen showing slight
asymmetry; (c), (d), Examples of very long specimens. The massive specimen is
unique on the site and illustrates the way in which the longest hand-axes were made
by striking of a very large flake, subsequently narrowed in trimming to give the
shape of the more typical long specimen also shown.
At the Heart of the African Acheulean: Kilombe 26
8. Discriminant Analysis of bifaces: a plot of Function 1 and Function 2, based on
selected sites from Africa, and the Middle East using 11 variables. Most Kilombe
biface assemblages are highly similar to one another, forming a tight cluster, but in
this analysis one Main Site area (Z) groups more closely with heavy duty
assemblages from distant sites. KW (Kilombe GqJh3 West), although above the 3-
banded tuff, falls within the main group. These are examples of Acheulean
‘variable sameness’ extending through space and time. Other sites: CORB =
Cornelia, basal; CORU = Cornelia Upper; VHOLS=Vaal Holsdam; VDOUG =
Vaal, Douglas; Umm Q = Umm Qatafa; KFA=Kalambo Falls A6; KFB=Kalambo
Falls B4; KAR U=Kariandusi Upper; KARL = Kariandusi lower site; STIC=Sidi
Abderrahman. See Gowlett (2012), Lycett and Gowlett (2008) and Table 3 for
further details.
At the Heart of the African Acheulean: Kilombe 27
Tables
Site
N=
Length
Breadth
Thickness
B/L
ratio
Correlation
B & L
Kilombe
394
149 ± 31
90 ± 16
42 ± 10
0.61 ± 0.07
0.84
Kariandusi
Upper Site
(obsidian)
60
149 ± 31
79 ± 13
37 ± 7
0.64± 0.09
0.77
Kariandusi
Lower Site
(trachyte lava)
126
149 ± 31
94 ± 11
49 ± 9
0.58 ± 0.07
0.59
Kariandusi,
All
186
152 ± 30
90 ± 14
45 ± 10
0.60 ± 0.08
0.77
Table 1: Summary of key data, expressed as means and standard deviations.
Correlation coefficients shown in the right hand column are not discussed in text, and merely
show that there is normally a very strong relationship between Length and Breadth.
Kilombe EH
N = 106
Kilombe GH
N = 54
Length
Breadth
Thickness
T/B
B/L
Weight
152 ± 30
94 ± 18
43 ± 10
0.47 ± 0.12
0.62 ± 0.07
545 ± 265 g
135 ± 33
81 ± 15
45 ± 13
0.55 ± 0.11
0.61 ± 0.09
412 ± 254 g
Table 2: biface data from Kilombe EH and Kilombe GH illustrate differences in size and
shape that can occur on the single surface.
At the Heart of the African Acheulean: Kilombe 28
Table 3: Supplementary data for the Discriminant Analysis
Function 1
Function 2
Function 3
Eigenvalue
0.299
0.229
0.120
Variance accounted
for
36.8 %
28.1 %
14.7 %
Correlations
Length
Breadth
Thickness
BA
BM
BB
PMB1
PMB2
TA
TM
TB
0.750
0.652
0.747
0.293
0.518
0.525
0.419
0.550
0.416
0.674
0.668
0.371
0.267
-0.157
0.452
0.279
0.229
0.584
0.440
-0.235
-0.137
-0.365
0.297
0.264
-0.490
0.361
0.389
0.173
0.243
0.427
0.471
0.212
-0.173
