Coping with uncertainty: Neolithic life in the Dhar Tichitt-Walata, Mauritania, ( ca. 4000–2300 BP)

Abstract

The sandstone escarpment of the Dhar Tichitt in South-Central Mauritania was inhabited by Neolithic agropastoral communities for approximately one and half millennium during the Late Holocene, from ca. 4000 to 2300 BP. The absence of prior evidence of human settlement points to the influx of mobile herders moving away from the “drying” Sahara towards more humid lower latitudes. These herders took advantage of the peculiarities of the local geology and environment and succeeded in domesticating bulrush millet – Pennisetum sp. The emerging agropastoral subsistence complex had conflicting and/or complementary requirements depending on circumstances. In the long run, the social adjustment to the new subsistence complex, shifting site location strategies, nested settlement patterns and the rise of more encompassing polities appear to have been used to cope with climatic hazards in this relatively circumscribed area. An intense arid spell in the middle of the first millennium BC triggered the collapse of the whole Neolithic agropastoral system and the abandonment of the areas. These regions, resettled by sparse oasis-dwellers populations and iron-using communities starting from the first half of the first millennium AD, became part of the famous Ghana “empire”, the earliest state in West African history.

Full text

Surface geosciences (Palaeoenvironment)
Coping with uncertainty: Neolithic life in the Dhar
Tichitt-Walata, Mauritania, (ca. 4000–2300 BP)
Augustin F.C. Holl
Museum of Anthropology, The University of Michigan, Ann Arbor, MI 48109, United States
Received 21 April 2008; accepted after revision 8 April 2009
Available online 25 June 2009
Written on invitation of the Editorial Board
Abstract
The sandstone escarpment of the Dhar Tichitt in South-Central Mauritania was inhabited by Neolithic agropastoral
communities for approximately one and half millennium during the Late Holocene, from ca. 4000 to 2300 BP. The absence
of prior evidence of human settlement points to the influx of mobile herders moving away from the ‘‘drying’’ Sahara towards more
humid lower latitudes. These herders took advantage of the peculiarities of the local geology and environment and succeeded in
domesticating bulrush millet –Pennisetum sp. The emerging agropastoral subsistence complex had conflicting and/or
complementary requirements depending on circumstances. In the long run, the social adjustment to the new subsistence
complex, shifting site location strategies, nested settlement patterns and the rise of more encompassing polities appear to have
been used to cope with climatic hazards in this relatively circumscribed area. An intense arid spell in the middle of the first
millennium BC triggered the collapse of the whole Neolithic agropastoral system and the abandonment of the areas. These
regions, resettled by sparse oasis-dwellers populations and iron-using communities starting from the first half of the first
millennium AD, became part of the famous Ghana ‘‘empire’’, the earliest state in West African history. To cite this article: A.F.C.
Holl,C.R.Geoscience341(2009).
#2009 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Résumé
Gérer l’incertitude : vie néolithique dans le Dhar Tichitt-Walata, Mauritanie (ca. 4000–2300 BP). La falaise du Dhar
Tichitt, au centre sud de la Mauritanie, a été habitée par des communautés agropastorales néolithiques durant environ 1500 ans au
cours de l’Holocène récent, entre ca. 4000 et 2300 ans BP. L’absence de preuve antérieure d’un peuplement humain suggère un
afflux de pasteurs mobiles, fuyant l’assèchement du Sahara pour des latitudes méridionales, plus humides. Ces bergers ont profité
des particularités de la géologie et de l’environnement locaux et sont parvenus à domestiquer le mil chandelle –Pennisetum sp. Le
système de subsistance agropastorale a des exigences antagonistes et complémentaires selon les circonstances. À long terme,
l’ajustement social à ce nouveau système de subsistance, des stratégies changeantes de localisation des sites, des configurations
régionales intégrées des sites et l’apparition d’entités politiques plus englobantes semblent avoir été utilisés dans cette zone
relativement circonscrite, pour faire face aux aléas climatiques. Une période aride intense, au milieu du premier millénaire BP, a
déclenché l’effondrement du système agropastoral néolithique et l’abandon de ces régions. Celles-ci, repeuplées à partir de la
première moitié du premier millénaire AD par des populations éparses d’habitants d’oasis ou de communautés utilisant le fer, firent
C. R. Geoscience 341 (2009) 703–712
E-mail address: holla@umich.edu.
1631-0713/$ –see front matter #2009 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.crte.2009.04.005

partie du célèbre « empire » du Ghana, le premier état de l’histoire de l’Afrique de l’Ouest. Pour citer cet article : A.F.C. Holl, C. R.
Geoscience 341 (2009).
#2009 Académie des sciences. Publié par Elsevier Masson SAS. Tous droits réservés.
Keywords: Dhar Tichitt; Dhar Nema; Dhar Walata; Agriculture; Livestock; Intensification; Seasonality; Colonization
Mots clés : Dhar Tichitt ; Dhar Nema ; Dhar Walata ; Livestock ; Intensification ; Saisonnalité ; Colonisation
1. Introduction
The Dhar Tichitt, located at 188200–188270N and 98
050–98300W, is part of the sandstone cliff series of the
South-Central part of Mauritania in southwestern
Sahara (Fig. 1). The area was colonized by Neolithic
agropastoral communities starting from ca. 4000 BP.
They spread all along the sandstones cliffs and settled in
the Dhar Tichitt, Dhar Walata, Dhar Nema, and beyond
[1,5–7,12,13,15,20]. These groups settled on the cliff’s
top, along intermittent rivers courses, and interdunal
depressions, herding cattle and sheep-goat, cultivating
bulrush millet, hunting wild game, gathering wild grain
and fruits, and fishing in the available ponds and lakes.
The local Holocene climatic record points to a Humid
Early Holocene (ca. 10,000–7000 BP) with relatively
large size lakes in the Hodh. It was followed by an Mid-
Holocene Arid phase (ca. 7000–5000 BP) during which
most of the large lakes dried up and SW–NE oriented
dunes were formed almost everywhere, except in the
baten –cliff foot. A Mid-Holocene humid phase –also
known as Nouakchottian –is documented to have taken
place from ca. 5000 to 3000 BP [7–9,13,15]. It is during
this period that the characteristic climatic pattern of two
contrasted seasons, a more or less longer dry season and
a generally shorter rainy season, appears to have
developed. The later portion of the Late Holocene,
particularly from 2500 BP on, was characterized by a
shift toward increased aridity with successive drought
episodes. These circumstances triggered the abandon-
ment of the area for wetter regions in the south and east.
How did Late Holocene people cope with the intrinsic
unpredictability of climatic parameters such as seasonal
variations, droughts, or flood during their more than
1500 years occupation of the area? This article,
following the perspectives outlined in environmental
archaeology research [7,13,16], tackles this issue
through the lens of the Dhar Tichitt, Dhar Walata and
Dhar Nema archaeological record and attempts to
decipher the actual coping strategies devised by
Neolithic agropastoralists. The emphasis was placed
on methods and theory in the original formulation of an
environmental archaeological approach to the evolution
of past societies. In a recent shift, exemplified in this
paper, the subdiscipline focuses more on results and the
‘‘relevance of these results for major themes and
research problems’’ in archaeology and anthropology
[13,16].
2. Holocene environment
Palaeoclimatic research in ancient lacustrine depos-
its found in different parts of the Dhar Tichitt [7–9,15]
has allowed a general reconstruction of the main
outlines of the regional environment during the last
10,000 years. Three kinds of lakes have been
documented all over the study area:
piedmont lakes set at the cliff foot on impervious
sedimentary formations that collect rain water from
their catchment basin (Fig. 2);
interdunal lakes created by both the rising water-
tables and rainfall;
hydrographic lakes fed by local network of streams
and rivers. There are nonetheless some intermediate
kinds of lakes that combine piedmont and interdunal
characteristics as is the case at Tichitt oasis and
Khimiya further east.
Evidence for a relatively large Early Holocene lake
measuring approximately 100 km west-east was found
between the Dhar Ousen (188200N and 108450W) in
the west and the Dhar Tichitt (188200N and 88550W) in
the east. The sandstone cliff was its northern shore but
its southern limits have not yet been traced with
precision [8,9]. With significant variations in size and
depth, it lasted from ca. 9500 to 7000 BP. The diatoms
flora consists above all of Melosira sp. in association
with Cyclotella kutzingiana,C. ocellata,Cymbella
gastroides and Rhopalodia parallela.Melosira is a
planctonic species of deep and extended water bodies.
Melosira italica is a northern alpine species and
Cyclotella ocellata is a boreal one [17]. The climate
was wet and cool with a more even distribution of
rainfall. The large lake evolved into lagoons and was
split into smaller independent lakelets.
All the lakes dried out during the Middle Holocene
Arid phase (ca. 7000–5000 BP), a period that witnessed
A.F.C. Holl / C. R. Geoscience 341 (2009) 703–712704

the accumulation and build up of very extensive and
thick deposits of eolian sands.
Late Holocene interstratified clayey and sandy
deposits point to a climate with contrasted seasons.
Small lakes dotted the landscape surrounded by rings of
high grass and trees as indicated by the high density of
fossil roots (Fig. 2). The recorded diatomite flora is
made of tropical epiphyte and littoral species such as
Amphora ovalis,Epithemia argus,E. sorex,Navicula
oblonga,N. Radiosa and Rhopalodia gibba. These
species thrive in shallow water tending to brackish.
Additional evidence, from pollen analyses and
faunal remains, was harnessed to achieve a higher
resolution in the reconstruction of the main character-
istics of the Dhar Tichitt Late Holocene environment.
Most of the analyzed pollen samples were collected from
contexts in direct association with archaeological
remains. Gramineae,Cyperaceae and Chenopodia-
ceae/Amaranthaceae are largely predominant among
non-arboreal pollen. The tree component is made offour
species only: Acacia sp., Balanites egyptiaca,Cappar-
idaceae sp. and Combretaceae sp. The pollen analyses
point to a vegetation with an important grass and shrub
stratum with scattered trees [7]. Animal bones on
the other hand point to a broader ecotonal situation.
Beside domestic animals, the faunal material reveals
habitats ranging from fresh water lakes and streams to
desertic environment. Fish [Lates niloticus], crocodile
A.F.C. Holl / C. R. Geoscience 341 (2009) 703–712 705
Fig. 2. Diatoms deposit from the piedmont lake at the foot of
Akhreijit Site cliff (Author’s photo).
Fig. 2. Dépôt de diatomées du lac de piémont, au pied de la falaise du
site d’Akhreijit (photo de l’auteur).
Fig. 1. Location of the Dhars in southern Mauritania: from west to east, the Dhar Ousen, Dhar Tidjikja, Dhar Tichitt, Dhar Walata and Dhar Nema
(Source: Google Earth).
Fig. 1. Localisation des Dhars dans la partie méridionale de la Mauritanie : de l’ouest à l’est, les Dhars Ousen, Tidjikja, Tichitt, Walata et Nema
(Source : Google Earth).

[Crocodylus niloticus], python [Python mollure] and
Hippopotamus amphibious are from water habitats. Four
species of large gazelles and antilopes living preferen-
tially in woodland and grassland with regular water
requirement are represented (Table 1,Figs. 3 and 4). Six
species, including two carnivores, rhinoceros, equids,
large gazelles, and large antilopes with varying water
requirements live more often than not in a grassland and
light bush environment. Animals that roam the desert and
are resilient to water shortage are represented by the
addax, small gazelles and Genetta genetta (Table 1). All
these environmental indicators point to wetter climate
than the present with, however, contrasting seasons
[2,5–9,12,13].
A.F.C. Holl / C. R. Geoscience 341 (2009) 703–712706
Fig. 4. Variation in the distribution of faunal remains according to
animal habitats as reflected in each sample.
Fig. 4. Variation dans la répartition des restes fauniques selon l’habi-
tat des animaux, tel que le reflète chaque échantillon.
Table 1
Faunal remains arranged after preferential animals habitats.
Tableau 1
Restes fauniques présentés selon les habitats préférentiels des ani-
maux.
Taxa Site 38 Site 46 General
survey
DN4
Domestic Animals
Bos taurus 35 5 32 139
Ovis/capra 12 2 14 5
Water
Fishes –5 2 508
Lates niloticus –5- +
Clarias sp. ––2+
Reptiles
Crocodylus niloticus –1–1
Python mollure ––1
a
–
Woodland and grassland: regular water requirements
Hippopotamus amphibious –27 –
Hippotragus equinus 265 –
Phacochoerus aethiopicus –-- 3
Kobus sp. 2 –– –
Tragelaphus sp. 3 2 ––
Taurotragus derbianus 525 –
Grassland and light bush: varied water requirements
Acinonyx jubatus ––1–
Ceratotherium simum ––1–
Equus sp. (asinus?) 121 –
Gazella dama 325 –
Oryx algazel 11 5 6 5
Redunca redunca ––– 2
Panthera leo 1–– –
Desert environment: resistant to water shortage
Addax nasomaculatus 943 –
Gazella dorcas/Gazella sp. 81 12 6 36
Genetta genetta 1–– –
Others
Struthio camelus –1–1
Bovidae sp. 45 21 18 63
Cercopithecus aethiopicus ––– 1
Cricetomys sp. 1 –– –
Mellivora capensis 2–2–
Total 214 77 111 764
Faunal remains and habitats.
a
Skull and numerous vertebras in anatomic connection suggesting
natural death.
Fig. 3. The general distribution of faunal remains according to
animal habitats.
Fig. 3. Répartitions générales des restes fauniques, selon l’habitat
des animaux.

3. The Neolithic occupation of the Dhars
There are a few scattered stone tools, handaxes and
flakes, assigned to the Early Stone Age [20]. All are
surface finds difficult to interpret. There is no evidence
of Late Stone Age occupation of the Dhars. Accord-
ingly, there may have been an influx of new populations
that had already mastered livestock husbandry of cattle
and sheep/goat. These groups that were moving away
from the drying Late Holocene Sahara found suitable
environmental conditions in the Dhar Tichitt, Dhar
Walata and Dhar Nema at the beginning of the second
millennium BC [1–3,5–7,12,15]. These conditions,
probably linked to the presence of high aquifers,
monsoonal rains and vestigial lakes, allowed for the
Neolithic occupation to take root and prosper. How did
they cope with climatic uncertainty and what does
this entail? The key element at this juncture was the
presence of water. It could be obtained through
rainfall, lakes, rivers, streams and springs. The positive
fluctuations of the aquifers could also make life
sustainable despite low rainfall level. In general,
however, there may have been a combination of rainfall
and water-table fluctuations to support Neolithic life in
the Dhars. The timing, quantity and distribution of
rainfall are some of the crucial variables in the
A.F.C. Holl / C. R. Geoscience 341 (2009) 703–712 707
Fig. 5. Radiocarbon chronology of the Dhar Tichitt settlements [7].
Fig. 5. Chronologie radiocarbone des peuplements du Dhar Tichitt [7].

sustainability of human life along the Saharan margins.
They affect agriculture, livestock husbandry, as well as
wildlife in general and in the absence of hydraulic
engineering capabilities are in fact the controlling
factors of human success or failure. The timing,
distribution and quantity of rainfall are fundamentally
unpredictable from one year to the next. How did
Neolithic people from the Dhars handle these unpre-
dictable variables? The Neolithic occupation of the
Dhars lasted from ca. 2200 BC to 4/300 BC. Their sites
were distributed in different ecological zones, in the
sandy lowland, the front of the cliff escarpment, and the
secondary and tertiary valleys of the hydrographic
network (Figs. 5 and 6). The pace of settlement
expansion will be dealt with later but at this stage
suffices it to state that the occupations of all the regions
ecological niches were contemporaneous (Fig. 7).
3.1. Intensification
Significant progress has been made in research on
early West African agriculture [3–5,7,10,12,14,18,19].
But the genesis of West African grain farming is
nonetheless still poorly understood in terms of the
dynamic processes involved. Domesticated millet –
Pennisetum glaucum –dated to the beginning of the
second millennium BC has been found in the Dhar
Tichitt [12], Dhar Walata in Mauritania [3] and the
‘‘Kintampo’’ site of Birimu in North-Central Ghana
[19]. A second wave of evidence pointing to the
cultivation of domesticated millet dating to the turn of
the first millennium BC has been documented at such
A.F.C. Holl / C. R. Geoscience 341 (2009) 703–712708
Fig. 6. Radiocarbon chronology of the Neolithic occupation of Bou
Khzama (Dhar Nema 4, Date BC).
Fig. 6. Chronologie radiocarbone de l’occupation néolithique de Bou
Khzama (Dhar Nema 4, datation BC).
Fig. 7. Patterns of settlement expansion in the Dhar Tichitt-Walata from ca. 2000 to 400 BC (Source: Holl 2004).
Fig. 7. Diagrammes d’expansion du peuplement dans le Dhar Tichitt-Walata ca. 2000 à 400 BC (d’après Holl 2004).

places as Oursi in Burkina Faso, Gajiganna in Nigeria
[14], suggesting a wide spread adoption of millet that
reached the rainforest and East Africa during the first
millennium BC. Domesticated African rice, Oriza
glaberrima, is attested at Jenne-Jeno in the second half
of the first millennium BC. The concept of intensifica-
tion refers to a range of strategies aimed at securing a
stable and reliable resources supply. It has two divergent
implications. In one set of strategies, sustainability
would be achieved through the broadening of collected
resources –stretching the diet-breadth in both plant and
animal resources. The other strategies set operate on a
narrow range of resources that experience a strong and
sustained exploitation pressure. In a co-evolving
conundrum, the selected plant or animal went through
a cascade of directional change that alters some of their
characteristics; non-shattering and in the longer run
larger grain for wild Pennisetum for example, or
reduced body-size for some mammals.
The Dhar Tichitt has been hailed as an interesting
case of local intensification that resulted in the
domestication of wild millet. Relying on P. Munson
[12,13], Stemler [18] offers the most coherent rendering
of the intensification theory. Starting with a question,
she wonders if it is ‘‘possible that it was the adoption of
herding and the extensive use of wild grain that initiated
the population growth indicated in the archaeological
record at Dhar Tichitt?’’ She then moves on to argue
that ‘‘if so, this change in the economy may have
resulted in the necessity for increasingly labor-intensive
practices to provide sufficient food for a growing
population’’, and concludes that ‘‘this trend eventually
resulted in the highly intensive interaction between
plants and people that we call agriculture’’ [18].
From this perspective, bulrush millet was part of a
cohort of wild plants that included Cenchrus biflorus
(cram cram), Brachiaria deflexa,Panicum turgidum,
P. laetum, exploited by Akhreijit Phase (ca. 1750 BC)
foragers. The shifting frequencies of different species
culminating in a 61% proportion of bulrush millet
impressions in potsherds from the Chebka phase (ca.
1000–900 BC) is supposed to illustrate the gradual
domestication of this species and the shift to the practice
of agriculture. The domesticated millet from Oued
Chebbi in the Dhar Walata dated to the beginning of the
second millennium BC [1–3] shed serious doubt on the
gradualist model alluded to above and makes it very
unlikely. There is not yet any convincing evidence for
the presence of Late Holocene mobile foragers
settlements in the Dhars. The domestication of
Pennisetum glaucum was probably an unanticipated
result of semi-nomadic herders exploitation of local
resources. Contrary to the other equally exploited wild
plants, wild Pennisetum adjusted to the regular and
sustained exploitation by both humans and livestock.
This adjustment resulted in the growth of non-shattering
large grain varieties that became humans staple food.
Despite the sustained presence of Pennisetum glaucum
remains in the Dhar Tichitt and Dhar Walata archae-
ological record, the importance of this grain in Neolithic
people diets cannot be assessed accurately. Plants
macroremains frequencies obtained from impressions
on pot-sherds cannot be translated directly into patterns
of past humans diets.
3.2. Seasonality
No evidence of hydraulic engineering –like well,
cistern and other water storage devices –has yet been
documented in the Dhars’ archaeological record.
Neolithic people certainly relied on springs, rain and
surface water that were available and availability was
very likely strongly constrained by seasonal variations.
Accordingly, one may well be founded to consider that
the landscape was lush green; springs and streams were
flowing, and lakes full of water during the rainy seasons.
This overall availability of water was altered progres-
sively with the onset of the long dry season. Some
streams may have dried up faster than others, and at the
peak of the dry seasons, a limited number of places may
still have had some water available. Such places were
generally found around piedmont and interdunal lakes
where the water-table allowed for the year-round
availability of water. Such places were focal areas for
settlement during the dry seasons, and many, like
Ngoungou (Site 45) in the Dhar Tichitt and Bou
Khzama (DN 4) in the Dhar Nema were used
intermittently for the whole duration of the Dhars
Neolithic occupation [5–7,16]. Bou Khzama, located in
the Dhar Nema at 1684402000 N and 781602600 W, is an
extensive surface site spread over tens of hectares. It sits
on a stabilized dune at some 200 m west of the cliff
escarpment. The site was sampled and excavated in
2001 and 2002 by a team led by A. Person [15]. The
excavated unit measured 140 m
2
and revealed a number
of archaeological features including hearths, burials,
pits, stone caches, iron smelting furnaces, slag heaps,
etc. The site is clearly a palimpsest that resulted from
intermittent and successive occupations over more than
three millennia, from ca. 2280–2060 BC to 1220–
1380 AD (Fig. 6). Bou Khzama, located next to the
mouth of a seasonal stream, was very likely used as dry
season camping area by groups of herders, hunters,
fishermen during the Neolithic occupation and later by
A.F.C. Holl / C. R. Geoscience 341 (2009) 703–712 709

iron-using communities at the time of the Ghana
kingdom.
Faced with a predictable dry season water shortage,
the Dhars Neolithic people devised a robust strategy to
enhance their livelihood, a short range and pulsatory
nomadism. Water sources were most of the time at a
‘‘walking’’ distance range. Groups could have walked
up to 5–10 km to fetch water in large clay vessels or
‘‘goat-skins’’, to be kept in large storage jars in the
‘‘household compound’’. Groups of herders probably
took livestock herds to dry season camping areas for
most of the duration of the dry season. They left their
traces in the archaeological record in the form of
shallow scatters of food waste, broken sherds and grain
processing stone tools [5–7]. Following this rationale,
the sites located on the cliff, all built with dry stone
masonry, were permanent villages of more or less linked
communities. Dry season camps on the other hand, all
aggregation points located in the sandy lowland, may
have shifted from place to place following the pace of
drying of surface water. Some of these sites with longer
lasting and reliable water supply were resettled years
after years. With the onset of the summer rains –June-
July –the dispersed groups of herders moved back to
their respective villages, pen the livestock in large
corrals and shift to the preparation of the fields for the
millet growing season. The combination of hunting,
fishing, livestock husbandry, agriculture, as well as
other crafts including pottery, stone tools making, etc.,
exerted a considerable demand on households’ labor
pools. How did these societies handle these conflicting
schedules?
4. The dynamics of agropastoral economy, site
layout and household structure
Mixed agropastoral economies combine in varying
degree, agricultural activities, livestock husbandry,
hunting, fishing, wild plants gathering and many other
crafts. In the yearly cycle and depending on climatic
parameters, all the activities mentioned above have
period of low and high labor demands. The scheduling
of productive activities and the corollary allocation of
labor require well-tested social mechanism to cope with
life during the Late Holocene in the Dhars regions of
Mauritania and elsewhere. Alliance building, household
structure and patterns of inheritance are such mechan-
isms that operate more or less as labor recruitment and
retention devices. The multiplicity of simultaneous
and/or successive tasks required for the smooth
operation of mixed agropastoral economy can hardly
be handled by a nuclear family. Cooperation along
task-specific groupings and/or age-sets could help
households navigate acute labor shortage and activities
bottlenecks. They are however difficult to document
in the archaeological record. Nonetheless, habitation
features from permanent villages provide a number of
clues on the solutions devised by Neolithic settlers of the
Dhars during the Late Holocene. While dry season sites
were characterized by scattered surface remains,
permanent villages located on the cliff point to a heavy
investment in habitation facilities construction. The
standard Neolithic household unit –a compound –part of
an intricate village layout including narrow streets
and open plazas was delineated by a dry-stone wall,
surrounding a number of dwelling units and storage
areas. In most of the cases, each unit had a single hearth
and one or many storage areas and was part of a cluster of
connected compounds, those sharing walls. The number
of dwelling units per compounds that varies from two
to nine at Akhreijit where a systematic inquiry was
conducted. It suggests that each of the compounds was
inhabited by a multicellular family unit, an extended or
polygamous family [6,7]. Such social units allow for an
optimal recruitment, retention and allocation of labor and
at the same time enhance the status of those able to attract
a large following. In this perspective, wealth and prestige
are materialized by the number of dependents.
4.1. Patterns of settlement
The reconstitution of the main patterns of the
expansion of settlement in the Dhar Tichitt-Walata is
partly inferential as a limited number of sites have been
excavated and dated. The new research on the Dhar
Nema [15] is not yet fully published. Research on the
Dhar Tichitt settlement sequences [5–7] was instru-
mental in developing this model (Fig. 7). Large villages
and large dry season camps, measuring more than
5 hectares, were all settled from the very beginning of
the Dhars Neolithic occupation around ca. 2200–
2000 BC. The settlement probably started with a small
number of settlers. They were distributed in three main
‘‘clusters’’ set at 40–50 km. The western part of the
Dhar Tichitt had a higher density of settlement right
from the beginning. Population growth was relatively
slow as the Early Settlement Sequence lasted for more
than 1000 years, from ca. 2200/2000 BC to 1200/
1000 BC. The location of all the pioneer sites was
optimal, along the escarpment and at the intersection of
the sandy lowland and the cliff top. Significant
population growth and the foundation of new smaller
villages took place mostly in the western confines of the
Dhar Tichitt with however a new settlement at Chegg el
A.F.C. Holl / C. R. Geoscience 341 (2009) 703–712710

Khail in the central part during the Middle Settlement
Sequence ca. 1200/1000–700 BC (Fig. 7). The distance
between sites groups was then reduced to 20 km in the
Dhar Tichitt. Small villages and hamlets spread all over
the landscape, precisely along the secondary and
tertiary valleys, during the Late Settlement Sequence
ca. 700–400 BC. All of this growth took place in the
central and eastern part of the Dhar Tichitt-Walata.
Subregional clusters of settlements with one large
central village, a few small villages and numerous
hamlets emerged during this sequence. Dakhlet el
Atrouss, at the center of the study area, reached
95 hectares in surface extent. Chebka, Akhreijit and
Khimiya in the west were protected by a perimeter wall.
The average territory per settlement dropped from
466.66 km
2
in the Early Settlement Sequence to
31.11 km
2
in the Late one. Competition for land may
have triggered conflict in the west. The colonization of
the cliff top helped to alleviate the pressure on land and
resources of the optimal zone where evidence of conflict
is manifest by the presence of perimeter walls.
5. Conclusion
The details on the initial colonization of the Dhars
are not known. But it is nonetheless clear that groups of
cattle and sheep/goat herders settled along the
sandstone cliffs at the end of the third millennium
BC. They devised successful strategies to cope with the
overall unpredictability of the climatic parameters.
Through sustained intensification, short range and
pulsatory nomadism, and colonization they succeeded
in building the earliest extensive village communities of
West Africa. The middle of the first millennium BC
witnessed the onset of an acute arid phase that
precipitated the disaggregation of the Neolithic
agropastoral occupation of the Dhars. The abandonment
of the whole area was probably gradual with small
groups of families moving south and southeast in search
for better environments. These populations may have
later contributed to the rise of the Ghana Empire. The
earliest settlers of Awdaghost were mobile herders [11].
Iron smelters settled in the Dhar Nema [15]. The
fluctuations in the level of Awdaghost aquifers, as
indicated by the increasing depth of wells from ca. 500–
600 AD to 1500 AD (Fig. 8), attest to the continuation
of long-term climate change that started at the end of the
1st millennium BC. The disruption of the Dhars water
cycle put an end to the most successful prehistoric
agropastoral economies of West Africa.
Acknowledgements
I wish to thank Professor S. Cleuziou and Dr. A-
M. Lezine for their invitation to write and present this
paper. My research in the Dhar Tichitt was funded by a
grant of the French Ministry of Cooperation to
Professor Henry-Jean Hugot. I am grateful to Dr.
Raymonde Bonnefille for her support and training in
pollen analysis and Dr. F. Poplin for training in faunal
analysis. Kay Clahassey from the University of
Michigan Museum of Anthropology helped with the
figures.
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