The Angevin-Aragonese Castle dominates Gaeta’s medieval centre and occupies an area of over 14,000 square metres. It consists of two buildings made in different periods but connected: at the bottom is the ‘Angioino Castle’, which houses a seat of the University of Cassino and Southern Lazio, while at the top is the ‘Aragonese Castle’, occupied by the Guardia di Finanza’s Nautical School.

Gaeta’s first castrum was built in the 6th-7th centuries AD, to defend the town from invasions by the Goths first and the Lombards later.

Frederick II of Swabia, who had stayed in Gaeta several times, had the castle fortified in 1223 because of its strategic position.  The works were completed in 1227, but only three years later the fortress was destroyed by rebels linked to the pope. In 1279, during the reign of Charles of Anjou, the Angevin Castle was built, characterised by a quadrangular plan with two tall conical towers.

Around 1430, Alfonso of Aragon established his seat in the castle, enlarging and fortifying the structure, including a throne room, flats and the mint of the Kingdom of Naples. In the early decades of the 1500s, Charles V of Habsburg further fortified the castle with new towers and bastions.

Gaeta and its castle were held by the Spanish until the beginning of the 18th century. In 1734, Charles III of Bourbon became the owner of the manor and made some restoration works. In the 19th century, the Castle often changed hands and suffered several sieges, including: the 1806 siege by French troops, the 1815 siege during the Austro-Napolitan war and the 1860 siege during the battles for the Unification of Italy.

The Aragonese side has a rectangular plan with three cylindrical towers at the apexes; until the end of the Second World War, it was home to a Carabinieri Cadet Battalion, today it houses the Nautical School of the Guardia di Finanza.

The Angevin sector, on the other hand, was used as a military prison from 1881 until June 1990. Conscientious objectors, political offenders and those convicted by the military authorities were imprisoned in it. Among the most famous inmates were Nazi officers Walter Reder and Herbert Kappler, who ordered the massacres at Marzabotto and the Fosse Ardeatine in Rome.

Inside the Angevin Castle, the rooms of the Bourbon cells, the royal chapel of Francis II Bourbon and the inner garden of Queen Maria Sofia are still preserved. During the siege of Gaeta in November 1860, the monarchs were forced to flee by sea through a secret passage in the castle. Today, the structure is used by the University of Cassino and Southern Lazio as a location for higher education, conferences, seminars and cultural events.