Located on two islands close to the shore at 180 miles south from Dar es-Salaam are the remains of two port cities, Kilwa Kisiwani and Songo Mnara. Kilwa Kisiwani has been occupied from the 9th century to the 19th century and saw its heyday between the 13th and the 14th centuries. These Swahili merchant cities prospered by controlling the maritime trade in the Indian Ocean with Arabia, India and China, trading ivory and gold from inland for silver, perfume, Persian earthenware and Chinese porcelain. The Portuguese built a fort at Kilwa Kisiwani during the 16th century.
Kilwa Kisiwani and Songo Manara show great archaeological evidence of the Swahili coastal culture and maritime trade that prospered along Eastern African coasts in the Indian Ocean from the medieval period to modern times. The sites are now registered (since 1981) on UNESCO's World Heritage List.