They were built during the last Carlist War (1872-1876), because as soon as Irún was threatened by the military actions of the Carlist troops, its City Council asked the Government to build various defense works. By Order of April 8, 1873, the execution of the defense works of Irún was authorized, on the condition that they had to be carried out in accordance with the instructions of the Corps of Military Engineers.
The plan of all of them is hexagonal between 3, 3 m and 3.5 m on each side, except the one located closest to Guadalupe, whose plan is square. They were all two storeys high and had a terrace; only the perimeter walls raised in sandstone are preserved, the interior is completely empty. On the ground floor some small rectangular holes were opened that served as ventilation and for observation.
Outside you can see a plinth of variable height, slightly wider than the tower and whose height above ground depended on its irregularities. Access was not made through the ground floor, but was opened on the first floor, which was accessed by a retractable staircase, in order to make access to the building more difficult. On this same floor two or three loopholes were opened on each side. The terrace is slightly advanced on the façade supported by three modillions on each side of the polygon and one at each vertex, opening an approximately circular hole between each of them that was used for the evacuation of rainwater.