Star-shaped military fort with four angular bastions. It features a low rectangular battery along the seaward-facing sides. The entrance, on the southeast wall, is preceded by a bridge (originally a drawbridge). In the center stand two oblong three-story buildings, connected by a covered wing, which housed barracks, warehouses, and the governor's residence. It includes a small chapel. It has a high battery facing south and sentry boxes at the corners of the bastions. Outside, it presents a wide moat with a counterscarp, covered way, and esplanade (now wooded). Its planimetry is considered "unusual" in the context of the Tagus bar fortifications, but it was the most important between the Citadel of Cascais and São Julião da Barra. The interior spaces preserve integrated heritage from the Estado Novo period, notably blue and white or polychrome tile panels with representations of national monuments or historical scenes. Post-1640 modifications indicate the appropriation and adaptation of the structure by the restored Portuguese Crown, integrating it into its own defensive strategy. The later presence of Estado Novo tiles demonstrates the continuous re-signification and use of the fort throughout different political regimes in Portugal.