In 1552 the studies and preparations began, but the construction order was dated June 15, 1554 according to a project by the engineer Juan Bautista Calví. The construction of the castle lasted for 20 years, although throughout the second half of the 16th century it was constantly evolving and improving its structure.
It was a square castle with bastions on the corners and in the uppor pont a wide flat terrace for the settlement of the artillery. The bastions were joined by a thick wall. The distance between vertices of adjoining bastions was 125 meters.
The solid wall had a width of 11 meters and attached to it, in its inner part, the different dependencies of the castle were located in a construction of two heights and 11 meters deep. The embankment at the top of the wall had a width of 22 meters. Being enclosed a patio of 40 meters of side, in whose center the well was located.
The outer part of the wall (scarp) began in a dry moat (15 meters wide) that surrounded the entire castle. On the outer wall of the moat (counter-scarp) there was a covered path with parapet and stockade, from which the surrounding terrain (glacis) was in full view.
For the construction of the castle, stone blocks of “marés” (characteristic island sandstone) were used.
It´s extraction was done under the castle´s own grounds. Tunnels were excavated, from wich stone blocks were extracted. As a result, a network of tunnels was dormed under the castle, that were used as warehouses and shelters
The initial garrison of the castle was about 120 men. In addition, it was ordered that in case of war, the garrison would be reinforced with 200 and 100 men from the Mahon and Alayor militias respectively.
The artillery initially assigned was, 8 past, 8 medium and 8 light guns, plus 16 muskets.