The introduction of the camel, which preceded Arabs and Islam by several centuries, brought about a gradual revolution in trade, and for the first time, the extensive gold, ivory, and salt resources of the region could be sent north and east to population centers in North Africa, the Middle East and Europe in exchange for manufactured goods. The civilizations that flourished in ancient West Africa were all based on trade, so successful West African leaders like myself tended to be peace makers rather than warriors. Caravans from North Africa crossed the Sahara beginning in the seventh century of the Common Era. Gold from West Africa was exchanged for something we as West Africans prized even more: salt. Salt was used as a flavoring, a food preservative, and for retaining body moisture. The empire owed much of its prosperity to trans-Saharan trade and a strategic location near the gold and salt mines. Both gold and salt seemed to be the dominant sources of revenue, exchanged for various products such as textiles, ornaments and cloth, among other materials. Many of the hand-crafted leather goods found in old Morocco also had their origins in the empire. The main centre of trade was Koumbi Saleh.