Situated off the coast of Tanzania, the island of Kilwa Kisiwani (“isle of the fish”) was once the center of one of the greatest empires in East Africa.

From the 9th century all the way up until the 19th century, Kilwa Kisiwani was a wealthy and powerful port, reaching its peak around the late-Middle Ages. At its height, the empire stretched from Kenya to Mozambique, and Kilwa Kisiwani’s prosperity was crucial to the development of Swahili civilization.

During this time great structures were built that are now stunning ruins, all that’s left of the late empire. One of the most impressive of the ruins is the Great Mosque, the oldest standing mosque on the East African coast, which has 16 domes supported by many arches and pillars. Another amazing site is the Palace of Husuni Kubwa, which overlooks the island from on high and was once the largest building in sub-Saharan Africa.

According to legend, the empire was established on the island by a Persian prince who bought Kilwa Kisiwani from an indigenous king for enough cloth to circle the island. The prince then destroyed a bridge that connected the island to mainland Tanzania.

Kilwa Kisiwani grew rich and powerful because it was well placed on trading routes between Africa, China, India, and Arabia. Gold, porcelain, quartz, ivory, and other valuable treasures all passed through the island. Among the island’s own exports were spices, tortoiseshell, and slaves.  The start of its decline came in the 16th century, when the Portuguese completed their own fort on the island and came to dominate trade in the region.