The fortress known in the dataset as Our Lady of the Cape was established at Cabo Frio in 1616, near the entrance to the Canal do Itajuru on Brazil’s Atlantic coast. Portuguese forces had recently expelled French settlers and their Indigenous allies from the region, whose brazilwood attracted competing traders. A permanent coastal strongpoint helped secure the new town, watch the channel leading to the Araruama lagoon, and assert imperial possession. Its history is generally associated with the fort now called São Mateus.

Builders placed the low stone-and-lime fortification on a rocky point beside the beach, where artillery could command vessels approaching the channel. Construction continued after the initial foundation, producing a compact bastioned work with thick walls, gun positions, internal rooms, and a small courtyard. Unlike towering medieval castles, coastal forts depended on fields of fire and close integration with shoreline geography. Soldiers, enslaved laborers, Indigenous workers, officials, and local suppliers all contributed to a defensive system extending beyond the masonry itself.

The garrison protected fishing, salt production, agriculture, and shipping around Cabo Frio while discouraging foreign trade. Its strategic importance rose and fell with changes in naval technology, regional settlement, and colonial administration. Repairs followed periods of neglect, and armament was adjusted as authorities confronted smuggling, privateering, and wider imperial conflicts. The fort also stood near routes through landscapes inhabited by Indigenous peoples whose displacement and resistance formed a fundamental part of Portuguese occupation, even when official military narratives minimized them.

During the nineteenth century the position gradually lost its original defensive purpose. Military use diminished, equipment was removed, and exposed walls suffered from wind, salt, sand, vegetation, and stone loss. The dramatic setting beside Praia do Forte nevertheless made the structure a local landmark. Heritage recognition and restoration campaigns in the twentieth century stabilized surviving fabric and adapted the site for public visitation and cultural activity. Some repaired sections reflect modern decisions, so interpretation must distinguish colonial construction, later alteration, and conservation.

Today the fortress anchors Cabo Frio’s historical waterfront and preserves evidence of the struggles that accompanied European colonization of the Brazilian coast. Maintaining mortar, drainage, masonry, and safe visitor access is a constant challenge in the marine environment. Its small scale should not obscure its significance: from this rocky point, Portugal sought to control a lagoon, natural resources, local movement, and rival empires. The monument also invites a broader account including Indigenous communities, coerced labor, soldiers, traders, and residents whose experiences made the colonial frontier.