Looking out over the harbor from which it was so often bombarded, this solid pile on the edge of the sea was built by the Portuguese over many years, commencing in 1593, and is the only genuine sight in Mombasa. Ironically, while the fortress was meant to symbolize Portuguese dominion over the Indian Ocean, it was built at a time when a Spaniard, Philip II, sat on the Portuguese throne, and it was designed by an Italian military architect named Cairati (working under his Portuguese nom de plume, João Batista Cairato).

His final commission, this was undoubtedly Cairati's finest achievement, incorporating High Renaissance ideas about the link between architecture and the symmetrical unity of the human form. Built directly onto a coral rock platform, the shape of the fort can be compared to a torso (the central portion) with four limbs (the bastions) and a seaward-facing head (the outworks). The design anticipated a shortage of manpower and was meant to disguise any evidence of this from potential attackers. The inherent simplicity of the classical form thus served to make the fort look a lot more imposing and indestructible than might have been the case.

Quite impenetrable by cannon fire, the fort left Portuguese control only after a 33-month siege by Omani forces; by the end of a brutal, long-winded struggle, an estimated 6,500 men, women, and children had lost their lives either in combat or to disease. At one stage, when reinforcements arrived, it was found that the fort had been under the defense of a young sheikh with a small band of Swahili soldiers and a mob of 50 women who had been trained to use muskets. When the British protectorate was proclaimed in July 1895, the fort was converted into a prison. It's been a national monument since 1958. Across the street is the Mazrui Graveyard, where the sheikhs who lived in the Fort and ruled the town autonomously from 1741 to 1837 are buried.