The dramatic 17-m pyramidal structure of the Tomb of Askia was built by Askia Mohamed, the Emperor of Songhai, in 1495 in his capital Gao. It bears testimony to the power and riches of the empire that flourished in the 15th and 16th centuries through its control of the trans-Saharan trade, notably in salt and gold. It is also a fine example of the monumental mud-building traditions of the West African Sahel. The complex, including the pyramidal tomb, two flat-roofed mosque buildings, the mosque cemetery and the open-air assembly ground, was built when Gao became the capital of the Songhai Empire and after Askia Mohamed had returned from Mecca and made Islam the official religion of the empire.