For more than 2,000 years, the Chadian Basin has been inhabited by agricultural and sedentary people. The region became a crossroads of civilizations. The earliest of these were the legendary Sao, known from artifacts and oral histories. The Sao fell to the Kanem Empire, the first and longest-lasting of the empires that developed in Chad's Sahelian strip by the end of the 1st millennium AD. Two other states in the region, Sultanate of Bagirmi and Wadai Empire, emerged in the 16th and 17th centuries. The power of Kanem and its successors was based on control of the trans-Saharan trade routes that passed through the region. These states, at least tacitly Muslim, never extended their control to the southern grasslands except to raid for slaves. In Kanem, about a third of the population were slaves.