Senegal was a part of the larger region called Upper Guinea by European traders. In the absence of written sources and monumental ruins in this region, the history of the early centuries of the modern era must be based primarily on archaeological excavations, the writing of early geographers and travelers, written in Arabic and data derived from oral tradition. Combining these data suggests that Senegal was first populated from the north and east in several waves of migration, the last being that of the Wolof, the Fulani and the Serer. Africanist historian Donald R. Wright suggests that Senegambian place-names indicate "that the earliest inhabitants might be identified most closely with one of several related groups—Bainunk, Kasanga, Beafada... To these were added Serer, who moved southward during the first millennium A.D. from the Senegal River valley, and Mande-speaking peoples, who arrived later still from the east." Probable descendants of Bafours were pushed southward by the Berber dynasty of Almoravids. Before the arrival of European settlers, the history of the Saharan region is mainly characterized by the consolidation of settlements in large state entities – the Ghana Empire, the Mali Empire and the Songhai Empire. The cores of these great empires were located on the territory of the current Republic of Mali, so current-day Senegal occupied a peripheral position. The earliest of these empires is that of Ghana, probably founded in the first millennium by Soninke and whose animist populations subsisted by agriculture and trade across the Sahara, including gold, salt and cloth. Its area of influence slowly spread to regions between the river valleys of the Senegal and Niger. A contemporary empire of Ghana, but less extensive, the kingdom of Tekrur was its vassal. Ghana and Tekrur were the only organized populations before Islamization. The territory of Tekrur approximates that of the current Fouta Toro. Its existence in the 9th century is attested by Arabic manuscripts. The formation of the state may have taken place as an influx of Fulani from the east settled in the Senegal valley. John Donnelly Fage suggests that Takrur was formed through the interaction of Berbers from the Sahara and "Negro agricultural peoples" who were "essentially Serer" although its kings after 1000 CE might have been Soninke (northern Mande). The name, borrowed from Arabic writings, may be linked to that of the ethnicity Toucouleur. Trade with the Arabs was prevalent. The Kingdom imported wool, copper and