Rocca di Ostia, Medieval fortress in Ostia Antica, Italy

Rocca di Ostia is a brick fortress with a triangular plan, built from 1483 for Cardinal Giuliano della Rovere, the future Julius II. Two round towers and a larger polygonal one, the tower of Martin V, stand at the corners and share a single wall walk. The walls are low, thick and sloped outward, with embrasures set low in the gorge; a papal apartment was added on the western side.

Cardinal Giuliano della Rovere, the future Julius II, began building the castle in 1483, and the work was completed around 1486. The design is usually credited to Baccio Pontelli, though Vasari named Giuliano da Sangallo and others have proposed Francesco di Giorgio Martini. The new structure absorbed the circular tower raised by Martin V between 1423 and 1424, which had served as a papal customs post watching the saltpans and river traffic.

The fortress combines military function with cardinal's residence, creating a structure that served both defense and displays of ecclesiastical power. This blend of fortress and palace shows how the Church projected authority over Rome's coastal gateway.

The fortress is open only on certain days and visits are typically part of guided tours through the archaeological park. Wear comfortable shoes and check opening times before arriving, as conditions can vary seasonally.

The monumental staircase inside the castle carries frescoes by Baldassarre Peruzzi showing mythological scenes linked to Hercules. They were painted for Cardinal Giuliano della Rovere, the future Julius II, who ordered the fortress built from 1483; Vasari instead credited the design to Giuliano da Sangallo.