Siege of Fort Jesus (1696-1698): Oman Takes Mombasa from Portugal

The siege of Fort Jesus was a 33-month blockade and assault of the Portuguese fortress at Mombasa, on the coast of present-day Kenya, by the forces of the Imamate of Oman under the Ya’ariba dynasty. It began on 13 March 1696 and ended with the capture of the fort on 13 December 1698. The fall of Fort Jesus ended Portuguese power on the East African coast north of Mozambique and made Oman the leading outside power on the Swahili coast.

Background: Portugal on the Swahili coast

The Portuguese arrived on the East African coast with Vasco da Gama’s voyage to India in 1498. They found a chain of wealthy Muslim trading towns, the Swahili city-states, such as Kilwa, Mombasa and Malindi, which linked Africa with Arabia, Persia and India.

Portugal tried to control this trade by force. Mombasa resisted and was sacked several times in the 16th century. In 1593 the Portuguese began building Fort Jesus to guard the harbour. Designed by the Italian architect Giovanni Battista Cairati, it was a modern artillery fortress built of coral stone, with angled bastions in the Italian style, and was largely complete by 1596.

The fort’s plan was carefully geometric. Its four main bastions and seaward projection give it an outline that has often been compared to the figure of a person lying down, reflecting Renaissance ideas of proportion. Thick walls, a dry moat cut into the coral rock and gun platforms covering both the harbour and the landward approach made it very difficult to take by direct assault.

Portuguese rule was never secure. In 1631 the ruler of Mombasa, Sultan Yusuf bin Hasan, who had been raised as a Christian in Goa under the name Dom Jerónimo Chingulia, turned against the Portuguese and killed the garrison. The Portuguese returned the following year.

The rise of Oman

In the 17th century Oman, under the Ya’ariba (Yaruba) dynasty, became a serious naval power. In 1650 the Omanis drove the Portuguese out of Muscat, their main base in Oman. Omani fleets then began raiding Portuguese positions along the East African coast, often invited by Swahili rulers who resented Portuguese control.

Through the second half of the century Omani attacks weakened Portugal’s position, and by the 1690s Fort Jesus was one of Portugal’s last strongholds north of Mozambique.

The siege, 1696-1698

An Omani fleet sent by Imam Saif bin Sultan I arrived at Mombasa in March 1696 and laid siege to Fort Jesus on 13 March. Inside the fort were a small Portuguese garrison and a much larger number of local allies and civilians, including Swahili people from Mombasa and nearby towns who had taken refuge there. Estimates of the total vary, but figures of around 2,500 people at the start are often cited.

The Omanis could not take the fort by storm, so they blockaded it. Inside, food ran short and disease spread. Contemporary accounts describe an epidemic, often identified as plague, which killed large numbers of the defenders, including most of the Portuguese. Over time many of the African allies also died or left.

Portugal’s viceroy at Goa sent several relief expeditions. They brought supplies and reinforcements in late 1696 and in 1697, which allowed the fort to hold out, but none was strong enough to drive away the besiegers. In October 1697 one relief ship, the frigate Santo António de Tanná, sank in the harbour beneath the walls of the fort.

By late 1698 only a handful of exhausted defenders remained. On 13 December 1698 the Omanis broke in and captured the fort. A Portuguese relief fleet arrived shortly afterwards, found the fort in Omani hands and withdrew.

Why the fort fell

Fort Jesus was not captured because its walls failed. It fell because the people defending it could not be kept alive. Several factors combined against the Portuguese.

• Distance: Goa, the Portuguese capital in Asia, lay thousands of kilometres away across the Indian Ocean. Ships depended on the monsoon winds, so relief could only be sent at certain times of year.
• Overstretch: The Portuguese Estado da India was already weakened by decades of war with the Dutch and by Omani attacks on other ports. It could spare only small forces for Mombasa.
• Disease and hunger: The blockade cut the fort off from the mainland. Epidemic disease and food shortages killed defenders far faster than combat did.
• Local politics: Swahili towns were divided. Some rulers and their followers sheltered in the fort and fought alongside the Portuguese, while others welcomed Omani support against Portuguese demands for tribute and trade monopolies.

Key people

• Saif bin Sultan I, Imam of Oman from about 1692 to 1711, who built up the Omani fleet and sent the expedition against Mombasa.
• The Portuguese garrison and its commanders, several of whom died of disease during the siege, leaving command to ever smaller groups of survivors.
• Swahili allies of both sides, whose choices helped shape the course and outcome of the war.

Consequences

The fall of Fort Jesus ended Portuguese rule on the coast north of the Ruvuma River, the modern border between Tanzania and Mozambique. Portugal kept Mozambique, but Mombasa, Pemba, Zanzibar and Kilwa came under Omani influence. Omani governors and garrisons were installed in the coastal towns, and Omani merchants increasingly dominated the trade in ivory, gold and enslaved people between East Africa, Arabia and India. For the Portuguese, the loss of Mombasa confirmed the long decline of their once dominant position in the western Indian Ocean.

The Portuguese briefly regained Mombasa in 1728, after a mutiny among the Omani garrison, but were expelled again in 1729. In the 18th century Mombasa was governed by the Mazrui family, nominally on behalf of Oman but often independently. In 1837 Sayyid Said, Sultan of Oman, took direct control, and he later moved his capital to Zanzibar.

Archaeology and legacy

Fort Jesus remained in use for centuries. Under British rule from 1895 it served as a prison. In 1958 it was declared a national park, and after excavations led by the archaeologist James Kirkman it was opened as a museum in the early 1960s. Inside, visitors can see Portuguese and Omani buildings, cannons and graffiti of ships scratched into the walls by soldiers.

The wreck of the Santo António de Tanná was excavated between 1977 and 1980, yielding guns, ceramics and the ship’s structure, now partly displayed in the fort. In 2011 Fort Jesus was inscribed on the UNESCO World Heritage List as one of the finest surviving examples of 16th-century Portuguese military architecture.

Timeline

• 1498, April: Vasco da Gama’s fleet reaches Mombasa and Malindi.
• 1593, April: Construction of Fort Jesus begins.
• 1631, August: Sultan Yusuf bin Hasan kills the Portuguese garrison of Mombasa.
• 1650: Oman expels the Portuguese from Muscat.
• 1696, 13 March: An Omani force begins the siege of Fort Jesus.
• 1697, October: The relief frigate Santo António de Tanná sinks off the fort.
• 1698, 13 December: Omani forces capture Fort Jesus.
• 1728-1729: The Portuguese briefly reoccupy Mombasa before final expulsion.
• 2011: Fort Jesus becomes a UNESCO World Heritage Site.

Why it matters

The siege of Fort Jesus marked the end of Portugal’s attempt to dominate the Swahili coast and the beginning of Omani influence that would culminate in the Sultanate of Zanzibar. It shows how Asian and African powers pushed back European expansion in the Indian Ocean long before the colonial era of the 19th century.