The most important extant structure at Gao is the Tomb of Askia at the Great Mosque of Gao, built in the 16th century for the caliph Askia Mohammed, the Songhai leader who converted Gao to Islam. ArchNet has a series of photographs of Askia and Gao.
Sources
Pekka Masonen. 1997. Trans-Saharan Trade and the West African Discovery of the Mediterranean. In M'hammad Sabour & Knut S. Vikør (eds), Ethnic Encounter and Culture Change. Papers from the Third Nordic Conference on Middle Eastern Studies, Bergen 1997: Nordic Research on the Middle East, vol. 3, pp. 116-142.
Susan Keech McIntosh. 1996. West African Savanna Kingdoms. In Brian Fagan (ed), Oxford Companion to Archaeology. OUP: London.

