The city lies on the southern edge of the Sahara, about 13 km from the Niger River. In the 14th–16th centuries, it was a major center of trans-Saharan trade and Islamic culture. It hosted renowned madrasas and libraries, including the Sankore University. The architecture features mud-brick mosques, narrow streets, and caravan courtyards. Despite its decline after the 16th century, the city remains a symbol of African scholarship. Home of the prestigious Koranic Sankore University and other madrasas, Timbuktu was an intellectual and spiritual capital and a centre for the propagation of Islam throughout Africa in the 15th and 16th centuries. Its three great mosques, Djingareyber, Sankore and Sidi Yahia, recall Timbuktu`s golden age. Although continuously restored, these monuments are today under threat from desertification.