Fortaleza de São Francisco Xavier da Ilha de Villegagnon, Military fortress in Rio de Janeiro, Brazil.

The Fortaleza de São Francisco Xavier da Ilha de Villegagnon is a military fortress on Villegagnon Island within Guanabara Bay, built with defensive walls and structures in Renaissance military style. Today it houses the Brazilian Naval Academy and maintains its original architectural design.

The French Fort Coligny, built by Nicolas Durand de Villegagnon in 1555 on the island of Serigipe, was destroyed by the Portuguese in the February–March 1560 campaign. A Portuguese position, possibly on the same foundations, was renovated in 1695 under Governor Sebastião de Castro Caldas. In September 1711 the powder magazine was hit by fire from René Duguay-Trouin's ships and exploded, destroying the structure, which then held twenty guns.

The fortress takes its name from Saint Francis Xavier, reflecting the deep connection between military protection and Catholic faith that mattered to early Portuguese settlers in the region. This religious naming tradition shows how spiritual values were woven into the colonial defense structures built during that era.

The area is only accessible through organized tours arranged by the Ministry of Marine, and visitors must register in advance. It is important to check current access conditions before planning a visit.

In September 1711, during René Duguay-Trouin's raid, artillery fire from his ships hit the powder magazine of the fort, which then held twenty guns of different calibres; the explosion destroyed the structure. A 1730 plan shows the position was still in use, and the larger fort begun in 1761 replaced it.