Santa Isabel Castle, in Pasai Donibane, is a fortress built in 1621 to protect the port of Pasaia.
The land on which construction of Santa Isabel fort was started was formerly occupied by a windmill (Churrutella-errota) built in 1450 on land allotted by Hondarribia. Instructions to build what are now the ruins of Santa Isabel Castle, were given by Emperor Charles I in the endeavour to protect the port against potential attacks by foreign warships or by the pirates roaming the area. The same Emperor had ordered construction of the tower standing until only a short time ago in Pasai San Pedro. The tower was built first, while Santa Isabel Castle in Donibane was completed under Philip IV. The castle had cannons aimed at the mouth of the port to warn off invaders crossing the port limit.
Although the fire from these cannons defended and was very well focussed on the port entrance, it couldn't offer any sort of protection whatsoever to the ships taking shelter there because they could be pursued right up until the rocks at the entrance, Arando Grande (belonging to Pasai Donibane) and Arando Pequeño (in San Pedro), started affording them protection against an artillery attack.
Santa Isabel Fort, almost impregnable from the sea, was therefore unable to defend itself against even the slightest overland attack. Thus, in 1638, Prince Conde made his way down from Jaizkibel to conquer Santa Isabel Castle with tremendous ease.
The fort stopped lending its services in 1867. The artillery platform was destroyed during the work carried out in the mid-20th Century to improve the entrance channel to the port, thus depriving the construction of its principal element.
The well-preserved remains of the ancient Santa Isabel Castle or Fort are silhouetted against the hillside in which its foundations are buried. It no longer looks like a fortress and today has no more than solid sandstone ashlar walls a few metres deep and the odd isolated tower. These walls have absolutely no openings whatsoever and are very high at some points. A private house has been built inside the fort.