Siege of Fort Jesus, Mombasa

The Portuguese built Fort Jesus at Mombasa in the 1590s to anchor their hold on the Swahili coast and its Indian Ocean trade. By the 1690s the rising power in those waters was Oman, whose Ya'aruba imams had already driven the Portuguese out of Muscat, and in March 1696 an Omani force laid siege to the fort. Disease did more damage than fighting: plague swept through the crowded garrison, and relief fleets from Goa arrived too small or too late. In December 1698 the Omanis stormed the walls and found only a few defenders left. The fall ended Portuguese power on the coast north of Mozambique and opened more than a century of Omani influence in East Africa, later centred on Zanzibar.

Fort Jesus is among the best preserved Portuguese fortifications of its age and has been a UNESCO World Heritage Site since 2011. Excavations there in the 1950s and 1960s, and underwater work in the 1970s on the Santo Antonio de Tanna, a Portuguese frigate lost in the harbour during a relief attempt, recovered much of what is known about life in the garrison. Swahili perspectives on the siege are thinner in the record than Portuguese and Omani ones, and historians have worked to recover the part played by the coast's own towns and rulers, who shifted between the two powers as interest dictated. The siege is also a starting point for arguments about how far the later Omani state at Zanzibar was a colonial power in its own right.