There would be three constructions that would be included under the name of Sant Jordi d'Alfama Castle, the old convent-castle, the modern fort and the optical tower, as all of them were of vital importance in coastal defense.
Today we know as the castle of Sant Jordi d'Alfama the one that corresponds to the fortification built between the end of the 17th century and the 18th century according to the new fortification system of the French Marquis de Vauman, who modernized the defenses of this coast, replacing the 'old convent-castle of Sant Jordi d'Alfama that the Castilian troops shot down with cannons in 1650, during the Reapers' War, to prevent the French and Catalans from fortifying there, as the place was a place of forced passage, both by land and by sea.
All that remains of the old medieval fortress-convent are fragments of the lower part of the walls and traces of others that would draw a plan adapted to the terrain. According to an inventory of 1576, it was a fortified body with a square plan (20 m side), centered by a courtyard around which were distributed the dormitory, the church and other typical dependencies of a convent (chapter, refectory... .). There was still a tower or watchtower that went up another four meters, reaching almost sixteen meters.
At the end of the 17th century and the beginning of the 18th, the defense of this coastal area was rebuilt following the so-called Vauman system, the military fort of Sant Jordi d'Alfama was born, which we know today as Sant Jordi Castle. Two thick parallel walls, united frontally by another in the form of a rare arch and a fourth wall where the entrance is located, protected by two advanced wall lines, delimit a polygonal central courtyard surrounded by a lattice of towers, bulwarks and revells.