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

Question: Why did the city become the holiest in the region
Self-contained rewrite: Why did Timbuktu become the holiest city in the Sudan region