Fort São Lourenço, Sea fort on the São Lourenço Islet, Island of Mozambique, Mozambique

Fort São Lourenço is a small triangular fort on the São Lourenço Islet beside the Island of Mozambique. It has two bastions, a curtain wall pierced by the gate-of-arms, and vaulted service rooms on its embankment. A ramp leads to the gun emplacements and bulwarks.

A first fort was built between 1587 and 1589 and demolished in 1595 by order of the Portuguese Crown. On its foundations a new structure was begun in 1695 under governor Dom Estevão José da Costa and finished in the first decade of the 18th century under Dom João Fernandes de Almeida. It defended the southwestern point of the port entrance, crossing fire with the Fortress of São Sebastião and the Fortim de Santo António, with twenty-two artillery pieces.

The fortlet takes its name from São Lourenço, the Portuguese form of Saint Lawrence, a dedication carried over from the earlier 1587–1589 fortification on the same islet. Its triangular plan with two bastions and the vaulted service rooms on the embankment are the features a visitor can still trace today.

Fort São Lourenço stands on the São Lourenço Islet beside the Island of Mozambique, so it is reached by crossing from the main island rather than by a walk along it. On the islet, a ramp leads up the embankment to the gun emplacements and bastions, and the gate-of-arms opens through the curtain wall linking the two bastions.

The fort's twenty-two artillery pieces were meant to cross fire with the Fortress of São Sebastião and the Fortim de Santo António on the Island of Mozambique, covering the southwestern point of the port entrance. The triangular plan with two bastions replaced an earlier fort of 1587–1589, demolished in 1595 by order of the Portuguese Crown.