Conversation so far:
why was timbuktu a major center of trade and cultural exchange
Timbuktu was located near the Niger River bend and so it was fed by the trade along both the east and west branches of this great water highway
Why was agriculture favorable in Timbuktu
The Niger River regularly flooded the plains between Timbuktu and Segu to the southwest, which provided fertile land for agriculture
Why did Timbuktu become the holiest city in the Sudan region
The combination of Timbuktu’s three mosques, clerical class, and universities meant that it became the holiest city in the Sudan region
What were the three great mosques in Timbuktu called
Its three great mosques, Djingareyber, Sankore and Sidi Yahia, recall Timbuktu's golden age

Question: What is the mosque made of
Self-contained rewrite: What is Djinguereber mosque made of