Founded in the 11th and 12th centuries to serve the caravans crossing the Sahara, these trading and religious centres became focal points of Islamic culture. They have managed to preserve an urban fabric that evolved between the 12th and 16th centuries. Typically, houses with patios crowd along narrow streets around a mosque with a square minaret. They illustrate a traditional way of life centred on the nomadic culture of the people of the western Sahara.