Introduction
Current archaeological information on early, large (>10 ha), nucleated village settlements in West Africa is still patchy and poorly understood. When and under what circumstances did societies increase in scale and organisational complexity? Research carried out since the early 1990s on Neolithic settlements in the Nigerian part of the Chad Basin has provided new information on this topic. Focused on the mosaic of sandy ridges and clayey deltaic soils formed on the south-western margin of Lake Chad as it retreated in the Late Holocene, this research program has delineated the dynamic settlement history of food-producing communities that migrated from the Sahara in the second millennium BC. Beginning with the arrival of pastoralists by c. 1800 BC, subsistence changed from a pastoral to an agro-pastoral production by at least c. 1200 BC. This development was apparently preceded by a shift to a more sedentary way of life around c. 1500 BC, as shown by the development of more substantial settlement mounds which existed until c. 800 BC.
Post-800 BC settlements are rather flat sites pointing to a pattern of settlement possibly ranging from seasonal camps to permanent villages. The 12-13 ha site of Zilum (Figures 1 and 2), dated to the mid-first millennium BC and described below, belongs to this latest category of settlements and is the key-site of the final phase of an archaeological tradition named Gajiganna Culture, c. 1800-400 BC (Reference BreunigBreunig 2001; Breunig et al. 1996; Breunig & Neumann 2002).
Map of the southern Lake Chad region showing the location of Zilum and contemporary sites.
View of the southern sector of Zilum showing millions of potsherds on the surface (Photo: P. Breunig).
This latest phase witnessed a near doubling of the size of the largest Gajiganna settlements, the apparent emergence of site hierarchies, a change in internal site organisation that included intensive pit-digging for house construction and for storage, and the appearance of a peripheral ditch-and-rampart system in the largest settlement (see below).
Characteristic of the Gajiganna Culture is a relatively thin-walled pottery with a predominantly zoned decoration made by comb impression, rocker comb, spatulate impression, incision and mat impression (Figure 3) (cf. Reference WendtWendt 1997). Though archaeologically recognised as a homogeneous ceramic tradition, there are spatial and time-sensitive attributes, as e.g. slip, temper and vessel types, that were employed for setting up a general chronological subdivision: Phases I, II and III, summarised in Table 1.
Gajiganna rim-potsherd displaying a zoned decoration of comb impressions and incisions (Photo: P. Breunig).
1 Reference BreunigBreunig 2001; Breunig et al. 1996; Breunig & Neumann 2002
Field work at Phase III sites has concentrated on the largest and most complex of the twelve known settlements of this period: Zilum (cf. Figure 1). Though dated to the mid-first millennium BC, a time when iron working is attested in the Chad Basin (Reference MaceachernMacEachern 1996; Quechón 2002), no clear evidence for the local use of iron has been found so far. Various excavations and a magnetic survey carried out in course of two field campaigns (2001/2002 and 2004) over an area of nine hectares show that the lack of iron was, however, not a factor that hindered the inhabitants in digging for construction and other purposes.
In contrast to the single pit known from a Phase II site (Reference GronenbornGronenborn 1997), the large number of pits found in Zilum is one of the most remarkable peculiarities of the settlement. The exact number of these features is unknown; however a figure of at least two thousand seems to be a reasonable approximation. Excavations and magnetic survey demonstrate that most of those pits are not arbitrarily distributed over the surface of the site, but arranged in a circular to oval manner often marking the limits of what seems to have been former compounds and huts/houses (Figures 4 and 5). Possibly several of those features served as borrow pits for obtaining clay used in the construction of houses and/or compound walls, but some, as indicated by their form, could also have served as underground storage facilities as is the case in the region today (Figure 6). Intensive pit-digging in the settlement possibly points both to an increased reliance on building with clay as opposed to thatch and to an increased preoccupation in storing food surpluses. Particularly in the apparently arid first millennium BC West Africa (cf. Reference McintoshMcIntosh 1998: 76; for summary on the climate of the Chad Basin cf. Reference SalzmannSalzmann 1999), the creation of food reserves may have been an important and vital strategy adopted for bridging potential years of reduced field yields in order of avoiding famine periods. In addition to storage of food in silos, the adoption in this dry period of a new cultivar and supposedly of a new farming system suitable for increasing crop yields (see below) can be seen as further strategic reactions for coping with those supposed risks.
A circular arrangement of pits (Photo: C. Magnavita).
A circular arrangement of pits possibly enclosing a former household area (Photo: C. Magnavita).
A probable mid-first millennium BC storage pit (Photo: C. Magnavita).
Ditch at the southern edge of Zilum (Photo: C. Magnavita).
Apart from borrow/storage pits, the evidence for digging activities in Zilum is manifested by two other kinds of features, the existence of which could only be assessed thanks to the magnetic survey. The first of these features are circular to oval trenches of several dozens meters extension, whence clay was most probably borrowed for building compound walls (Magnavita & Schleifer 2004). The second kind of feature consists of much larger curvilinear trenches running across and along the periphery of the settlement (Magnavita & Schleifer 2004). The longest and supposedly youngest of these last mentioned features has a depth between 0.9 and 2.8 m and a width of up to 6 metres (Figure 7). As this feature is seen in the magnetic mapping as encompassing the southern and eastern portions of the settlement, it is interpreted as a ditch dug for obtaining clay used in the construction of a long ago decayed rampart or wall that enclosed at least a large part of this 12-13 ha settlement (Magnavita & Schleifer 2004). The function of this enclosure is unknown, but due to the depth of the ditch and the relative large volume of earth borrowed for constructing the supposed rampart or wall (up to 5 cubic metres), a defensive or at least 'keep out' purpose can not be ruled out. As a communal project, this structure is the earliest of its kind in the Chad Basin and one of the earliest in whole West Africa. Seen in a social perspective, it shows the relatively high degree of organisational complexity achieved by the settlement's inhabitants.
As further archaeological evidence points out, this increased level in the organisational complexity seems to be also reflected at other areas of the communal life. In this context, discrete concentrations of ceramic tampers used in pottery production, grooved stones possibly used in the manufacture of beads/bone points, as well as several joined lined basins with a high content of sulphur figure as indications that craft production around the mid-first millennium BC Chad Basin may have developed from a purely household-related activity into an occupation performed by at least part-time specialists (Magnavita & Magnavita 2001). On the political sphere, the complexity of Zilum is emphasised by the presence of four contemporary, but substantially smaller sites (<1 to 3 ha) situated at distances between c. 2.5 to 4 km from Zilum (cf. Figure 1). These sites seem to figure as satellites that surrounded the central settlement. Apart from this cluster there are currently other seven known sites ranging from small (1 to 2 ha) to medium-size (4 to c. 7 ha). All in all, these sites apparently constitute what one could call a hierarchy of settlements.
Vigna unguiculata. Seed seen in ventral and lateral views (Photo: S. Kahlheber).
Preliminary studies of V. Linseele (Royal Museum for Central Africa, Tervuren, Belgium) on faunal remains from some of the excavated pits reveal that wild and domestic animals contributed to subsistence. Besides sheep, goat and cattle, wild mammals, birds, reptiles, fishes and molluscs are attested among the finds. The investigation of archaeobotanical remains undertaken so far adds some more information: domesticated Pennisetum glaucum, pearl millet, seems to have been the only cereal and the staple crop of the former inhabitants of Zilum. Seeds of Vigna unguiculata, the cowpea (Figure 8), confirm the cultivation of domestic pulses. Both crop species prefer well-drained soils, which are currently found in the sandy areas raised over the clayey plains and depressions. Today, such localities are subject to rain fed agriculture of mixed cropping systems of pearl millet and cowpea. Commonly used as a strategy to produce increased yields during intensification of agriculture (Reference FrankeFranke 1995), mixed cultivation might also have been practised at mid-first millennium BC Zilum as a way of improving the economical base of the thriving settlement. The fruits of wild woody species like Vitex sp., Ziziphus sp. and Celtis integrifolia provided a supplementary nutritional source, whereas the finds of Acacia nilotica might be related to the tanning process of manufacturing leather. Several tree species attested in the archaeobotanical record are rare or non-existent in the region today. Prosopis africana, one of the most common species preserved by charcoal, has not been observed in the vegetation surrounding the site. This tree yields excellent firewood and presumably has become rare due to over-exploitation. Other vanished species require moist to wet habitats, and their disappearance might be related to increasing aridity or to the introduction and farming of Sorghum (guinea corn) in course of the Iron Age (cf. Reference MagnavitaMagnavita 2002), the extensive cultivation of which must have largely affected the natural vegetation of the seasonally flooded clay plains.
It is unclear what exactly the archaeological evidence of Zilum and its contemporary neighbours reflects for the culture history of the Chad Basin and of West Africa in general. All in all, the size of the largest settlement, its presumably relative large population, the presence of public architecture, the apparent existence of discrete zones of production as well as the hierarchy of sites can be interpreted in a series of ways. One of these is to see Zilum, apparently the most complex of these mid-first millennium BC Gajiganna settlements, as a key-site showing early urban attributes and figuring as a central place (Magnavita & Magnavita 2001). The second is to consider the 1400 year-long development of the Gajiganna Culture with Zilum at its apex in a historical-particularistic, neo-evolutionist perspective with regard to the later emergence in the Chad Basin of socio-politically more complex societies of the chiefdom type (Reference MagnavitaMagnavita 2004). While making theoretical exercises for considering the meaning of the site in regional and supra-regional perspectives is not irrelevant, an important issue is the consideration that external factors as the supposed climatic constraints of the first millennium BC and consequently social upheavals, at least in this particular case, may have promoted the emergence of the large, nucleated and fortified settlement of Zilum. Is stress of any kind the motor leading to developments towards organisational complexity in sub-Saharan Africa and elsewhere? Though the current evidence from the Chad Basin seems to point to this way, further research is necessary for recovering more data on the triggers of this manifest complexity and for better assessing the historical significance of mid-first millennium BC Gajiganna settlements. Our next field campaign will be therefore focused on the search in Zilum and some of its satellites and neighbours for clues that might be useful in figuring out the character, economy and ecological setting of these mid-first millennium BC settlements.
