Although the term “arsenal” originally referred to places intended for the manufacture of warships, in the modern era the name was extended to warehouses for storing and repairing the weaponry of a fortress. The Roses arsenal was probably built at the end of the 16^th  century, taking advantage of a corner formed by the medieval wall, whose thickness served as protection in case of bombardment. It is a quadrangular building that had a main semicircular arch door, located to the east. The building had a first floor, with a wooden floor, and was covered with a double-pitched roof supported on a double row of quadrangular pillars. It seems that originally most windows were usually arrow slits . These elongated and very narrow openings, wider on the inside than on the outside to allow shooting, especially with bows and crossbows, are typical of the medieval era. Here,  they were probably used to provide some light and avoid the entry of sparks that could ignite stored ammunition in case of bombardment.

Subsequently, a second, elongated warehouse was added on the southern side. Throughout its existence, it underwent other reforms, such as the opening of new, larger doors and windows on the upper floor.