Great Mosque of Djenne, Mali
Djenné, the oldest known city in sub-Saharan Africa is the site of the world’s largest mud structure, the Great Mosque of Djenné. Little is known of the first mosque built in the eleventh century; construction began on the current structure in 1907, a replacement for an intermediate version that was allowed to fall into disrepair. The citizens climb on the horizontal posts annually to apply new mud, which preserves the mosque.