Mombasa Kenya, a city in eastern Africa 270 miles (435 km) southeast of Nairobi. It lies on Mombasa Island in an inlet of the Indian Ocean, and on the surrounding mainland. Mombasa is a terminal of the Uganda-Kenya railway and has one of eastern Africa's busiest and best ports at Kilindini Harbor. The explorer Vasco da Gama found Arab settlers here when he arrived in 1498. Fort Jesus, completed in 1595 as a Portuguese stronghold, fell to the Arabs in 1698. Britain leased Mombasa from the sultan of Zanzibar, 1887–1963.