The area of the city has evidence of settlements since the Palaeolithic era. The fertile lands of the Niger River Valley provided the people with an abundant food supply and early kingdoms in the area grew wealthy as they established trade routes linking across west Africa, the Sahara, and leading to northern Africa and Europe. The early inhabitants traded gold, ivory, kola nuts, and salt. By the 11th century, the Empire of Ghana became the first kingdom to dominate the area. Bamako had become a major market town, and a centre for Islamic scholars, with the establishment of two universities and numerous mosques in medieval times.