The Cardinal Giuliano della Rovere, who was called Julius II (1503-1513) when he became Pope, built this castle between 1483 and 1486 to protect the last bend of the river Tiber. This site had an important role for the control of the customs traffic along the river and for the salt pans that were in control of the Roman Curia.
The castle is one of the first example of military Renaissance architecture and the works were made by an architect form Florence called Baccio Pontelli. He used a lot of material coming from the excavations of Ostia Antica. It was chosen a particular plant with a triangular shape because of the conformation of the ground and the river Tiber, but also because it was important to preserve a pre existing tower which was built there by the Pope Martino V (1471 – 1431) to defend the area.
All the architectonic complex has a system of “casemate” (rooms for soldiers where they could shoot and where it is still visible a small bathroom). This links the main tower to other two towers, a small river and a big moat all round. All the entrances had drawbridges and the one on the small river still has a rolling shutter.
During the age of the reign of Julius II, the castle was used not only for defending but also as a residence on the west side of the building, on the court yard; it was also added a big stairs, with three flights, on which sides and ceiling it is still possible to see frescos of Baldassarre Peruzzi.