Gao was the capital of the Songhai Empire. The city was selected because of its strategic location in the trans-Saharan trade. Dia Kossoi, the fifteenth of Dia line, selected the area.
Davidson, Basil, Buah, F. K. ,and Ajayi, J.F. Ade(1966). A History of West Africa. Doubleday:New York, p. 67. Library of Congress Card #66-24317