Jenne-jeno is the site of the oldest known settlement in sub-Saharan Africa, dating from the third century B.C. Many scholars previously thought that complex social organization did not exist here before the arrival of Islamic traders in the seventh and eighth centuries. However, archaeological expeditions conducted in the 1970’s clearly showed that indigenous trade networks and social structures were in place starting from as early as 200 B.C. The old town of Djenne, Jenne-jeno, is located on an island in the inland Niger Delta of Mali. It was founded in 800 A.D. and at this time already had about ten thousand inhabitants. Between 800 and 1000, Jenne-Jeno was a thriving area, owing to the combination of rich rice-growing soils, levees for pasture in the flood season, deep basin for pasture in the dry season, and access to major river channels and the entire system of inland trade routes. Djenne later became an important Islamic cultural center, home to one of the largest mosques in the Sudanese building style, erected in the 13th century, and today a UNESCO World Heritage Site. After 1400, the town gradually declined, while the present-day Djenne, little more than one mile away, was already founded in about 1250.