Kilwa Kisiwani was once a massive Swahili port town. It was established in the 8th century and reached its peak from the 12th to the 14th centuries when it was one of the largest settlements in East Africa and an important hub in the Indian Ocean trade route.
A combination of rising sea levels caused by climate change and the removal of the mangrove forest have resulted in severe erosion at several of the monuments in Kilwa, including the Gereza.