Djenné, the oldest known city in sub-Saharan Africa, is situated on the flood lands of the Niger and Bani rivers, 354 kilometers (220 miles) southwest of Timbuktu. It has an ethnically diverse population famous for its mud brick architecture. The city was a centre of trade and learning, and has been conquered a number of times since its founding. It was designated a World Heritage Site by UNESCO in 1988.

The city was founded by merchants around 800 AD and flourished as a meeting place for traders from the deserts of Sudan and the tropical forests of Guinea. It was captured by the Songhai emperor Sonni 'Ali in 1468. The city developed into Mali's most important trading center during the 16th century because of its direct connection with Timbuktu by a river.  

In 1591, Morocco conquered the city after destroying Songhai's hold in the region. Moroccan kings controlled Djenné until 1780 and during these years, its markets further expanded featuring products from throughout the vast regions of North and Central Africa. In 1861, the city was conquered by the Tukulor emperor al-Hajj 'Umar and was then occupied by the French in 1893. Thereafter, its commercial functions were taken over by the town of Mopti, which is situated at the confluence of the Niger and Bani rivers.

Besides being known for its commercial importance, Djenné was also known as a center of Islamic learning and pilgrimage. The city attracted students and pilgrims from all over West Africa. Today, Djenné is an agricultural trade center with several beautiful examples of Muslim architecture. The inhabitants of Djenné mostly speak a Songhay variety termed Djenné Chiini.  

Today Djenné boasts of two tourist attractions: The Great Mosque and the weekly market, taking place every Monday. The Great Mosque was built in 1907 with rectangular sun-dried mud bricks that are held together by mud mortar and plastered over with mud. This earthen architecture, which is found throughout Mali, can last for centuries if regularly maintained.

The large market square brings together different ethnic groups: Bambara (farmers), Peul and Fulbe (cattle breeders), Bozo (fishermen and masons), Bella (firewood traders) to trade. Goods traded are cattle, meat, fish, vegetables, rice, household goods, and drugs among others. There is also Le campement, the only one place tourists can stay. It is located about 400 meters from the mosque.

Reference

http://www.globosapiens.net/travel-information/Djenne-644.html
http://goafrica.about.com/od/mali/p/djenne.htm
http://www.foto8.com/issue08/djenne03.html
http://www.sacredsites.com/africa/mali/djenne.html
http://en.wikipedia.org/wiki/Djenn%C3%A9