Mopti grew up where two rivers meet - the Niger and the Bani - on what was once a small Bozo fishing settlement. By the early 20th century it had become a thriving commercial port under French colonial administration, a hub linked downriver to Bamako and the wider trade of the Western Sudan. It was into this rising river town, in the Komoguel district, that the city built its Friday mosque between 1933 and 1935. The structure belongs to a tradition known as the mosques of the Niger valleys - earthen buildings raised by experienced masons and the collective labor of the community, a style born of trans-Saharan trade and the spread of Islam along its routes.

The mosque is a marvel of mud. Its symmetrical facades rise to a mihrab tower of 17 meters and lateral towers of 13.5, the whole structure covering some 530 square meters. There is no open courtyard - the prayer hall is enclosed, its roof carried on four bays of pillars set parallel to the qibla. Corner pillars and buttresses taper to elongated points; the northern and southern entrances open through Djennian portals. The towers climb to trapezoidal spires capped with ceramic crowns, and atop each, a pair of ostrich eggs - a recurring motif in Sahelian sacred architecture, symbols of fertility and purity. The toron that stud the walls double as a permanent scaffold for the annual replastering that keeps the earth intact.

Mud architecture is fragile, and good intentions can wound it. A restoration in 1980 introduced cement - baked brick added to the towers and corner pillars, a cement skin applied to the upper facades. It looked, perhaps, like progress. It was the opposite. Cement traps moisture against the earthen core and cannot breathe with the building as mud plaster does; the additions damaged the very structure they were meant to protect. The mosque that had stood for four decades, faithfully replastered by hand, now bore a hard shell that was slowly killing it from within.

Between 2004 and 2006, the Aga Khan Trust for Culture set out to undo the harm. Local masons - the inheritors of the very tradition that built the mosque - stripped away the cement layer and stabilized the upper structure, replacing damaged areas with traditional mortar and brick made by mixing earth with rice chaff. Completed in June 2006, the restoration returned the building to the materials it was meant to be made of: earth, water, timber, and the recurring care of the hands that maintain it. In 2009, Mali placed the mosque on UNESCO's World Heritage Tentative List, formal recognition of a building that had nearly been lost to the wrong kind of repair.