Corpus of early Arabic sources for West African history - J. F. P Hopkins

From the eighth century onwards, the Muslim townsfolk of North Africa were well aware that fifty stages away across the desert to the south lay a land inhabited by black people which was the source of gold, ivory and slaves. It was no mere rumour stemming from occasional journeys of special daring, as it had been in the time of Herodotus. For the Muslims, the black slaves were in their midst as labourers and soldiers, servants and concubines. And soon the passing caravans began to be swelled by black students and pilgrims, showing that the religion and civilization of Islam were spreading across the Sahara into the western and central Sudan...