Located on the south bank of the mouth of the port of Mahon, the Sant Felipe castle was designed by engineer Juan Bautista Calvi to defend the port against pirate raids and invasions. Its construction was initiated after the attack on the city of Mahon by pirate Barbarossa in 1535, when the city was razed and more than 3000 inhabitants were sent into slavery.
Initially, the castle had a square floor plan with four bastions on each of the corners and was surrounded by a moat. However, after the British conquest and the annexation of the island of Minorca to the British Crown in 1713, British engineers increased its depth and spaciousness by building new counterguards, ravelins and lunettes, as well as the corresponding moats which interconnected on different levels, around the old Spanish castle. This gave it its characteristic 8-pointed star shape and transformed it into one of the largest fortresses at the time.
It was conquered in 1756 by French troops and surrendered to Spanish troops in 1782, so Minorca was returned to the Spanish crown after a gruelling six-month siege. Carlos III ordered its demolition so that it would not lure foreign powers to the island. It was again recovered by the British in 1798, and it immediately underwent repair and rebuilding works. After the Peace of Amiens in 1802, Minorca was returned to Spain and the Sant Felipe castle was finally demolished and rendered unusable.
Nowadays it is possible to visit the outer works and the underground galleries, which have been partly rebuilt thanks to the efforts of the Consortium of the Military Museum of Minorca.