By the mid-first millennium a.d., Middle Niger cities took the form of many separate mounds clustered together. Many of these mounds may have been settlements of specialists. This distinctive city form may have had its origin in segmented, but articulated, Late Stone Age communities in the southern Sahara. The Pulse Model is an attempt to reconstruct the circumstances of environmental change and interactions among these communities that encouraged occupational specialization. The model predicts the best locations to search for evidence of early specialization, namely the several north–south trending palaeochannels of the southern Sahara. There, groups increasingly concerned with intensification of production within separate microenvironments would nevertheless have been in close contact. Climate shifts over the past several millennia create a ‘pulse’ of population movements, or shifts of ecological adaptations, along these long corridors. However, adaptation to climate change and stress incompletely explains the emergence of specialization. Tradition, myths, legends and material reinforcements of divisions between present-day ethnic and artisan groups in the Middle Niger suggest the ways in which corporate identity may have been constructed and maintained in the very distant past. If corporate identity can emerge in a form that discourages conflict between groups, the result might be increasingly specialized responses to climate change and to the economic and social opportunities of early urbanism. There should be no sharp discontinuity between the emerging specialization of the last millennia b.c. and the earlier clustered urbanism of cities such as Jenne-jeno. Middle Niger urbanism is an intensification of prehistoric social dynamics, not a revolutionary process.

This article reports over 250 new radiocarbon dates relevant to recent archaeological research in West Africa. Thanks to the continuing trend towards series of dates from either single sites or groups of related sites, some major blanks on the archaeological map of West Africa have been replaced by well-dated regional sequences. An example is the Malian Sahara, where palaeoenvironmental and archaeological investigations at a large number of sites have clarified the relationship between Holocene climatic change and Late Stone Age occupation. Other areas that were largely archaeological unknowns until the research reported in this article was undertaken include the middle Senegal valley, the Inland Niger Delta, and the Bassar region in Togo. Other research included here reinterprets previously studied, ‘classic’ Late Stone Age sequences, such as Adrar Bous, Kintampo and Tichitt. There are also new dates and details for early copper in Niger and Mauritania which prompt a reconsideration of the true nature of this proposed ‘Copper Age’. Of particular significance to general reconstructions of West African prehistory is the documentation of regional and long-distance trade accompanying the emergence of complex societies along the Middle Senegal and Middle Niger in the first millennium A.D.

The article begins with a brief commentary on calibration, in view of the recent publication of high-precision calibration curves. Several prevalent misconceptions of what calibration is and what it ought to do are addressed. We suggest that archaeologists and historians should routinely make reference to calibration in order to avoid misinterpreting radiocarbon results.

The dates and circumstances of early references to Jenne have led historians to conclude that the city originated relatively late in time. It is widely believed that the city developed simultaneously with Timbuktu in the mid-thirteenth century as an artifact of trans-Saharan trade. Persistent oral traditions of the foundation of Jenne in the eighth century are generally discounted.

Recent archaeological excavations at the ancestral site of Jenne-jeno have established that iron-using and manufacturing peoples were occupying the site in the third century B.C. The settlement proceeded to grow rapidly during the first millennium a.d., reaching its apogee between a.d. 750 and 1100, at which time the settlement exceeded 33 hectares (82 acres) in size. The archaeological data are supported by the results of site survey within a 1,100-square-kilometre region of Jenne's traditional hinterland. During the late first millennium a.d., several nearby settlements comparable in size to Jenne-jeno existed, and the density of rural settlements may have been as great as ten times the density of villages in the hinterland today.

Evidence from excavation and survey indicates that Jenne participated in inter-regional exchange relations far earlier than previously admitted. The stone and iron in the initial levels at Jenne-jeno were imported from outside the Inland Delta; levels dated to c.a.d. 400 yield copper, presumably from distant Saharan sources. The importance of the abundant staple products of Jenne's rural hinterland, including rice, fish and fish oil, is examined in a reassessment of the extent of inter-regional commerce and the emergence of urbanism during the first millennium a.d. Jenne-jeno may have been a principal participant in the founding of commercial centres on the Saharan contact zone of the Bend of the Niger, rather than a product of the luxury trade serviced by those centres.