A bastion is an angular structure projecting outward from the curtain wall of an artillery fortification. The fully developed bastion consists of two faces and two flanks with fire from the flanks being able to protect the curtain wall and also the adjacent bastions. Bastion fortifications offered a greater degree of passive resistance and more scope for ranged defense in the age of gunpowder artillery compared with the medieval fortifications they replaced.
The San Narciso, to southeast is the nearest Figueres, and Santiago, the Northeast, are equal to each other, are connected with the square and inside a store of gunpowder stands bombproof, whose vault is pointed and has interior buttresses. The Polvorín located in this bastion was destroyed in the bombing of 1939.