Songhai Empire was a state located in the western part of the Sahel during the 15th and 16th centuries. At its peak, it was one of the largest African empires in history. The state is known by its historiographical name, derived from its largest ethnic group and ruling elite, the Songhai people. Sonni Ali established Gao as the empire's capital, although a Songhai state had existed in and around Gao since the 11th century. Songhai rulers subsequently took advantage of the weakened Mali Empire to expand Songhai rule. Currencies: Great market places thrived in major cities where kola nuts, gold, ivory, slaves, spices, palm oil and precious woods were traded in exchange for salt, cloth, arms, horses and copper.