Declared a Site of Cultural Interest , the 260m section of the wall that falls on the right bank of the Palace´s river, is the only thing that is conserved. It was restored in 1996.
The mountain wall that surrounded Sant Mateu had a perimeter of 1,600 meters and eight access gates. It is masonry, variable thickness and has an average height of 6 meters including the crenels.
It is the second walled enclosure of Sant Mateu. It was built from 1357 to 1380 under the mastery of Pedro de Thous. It replaced the primitive wall of the 18th century that surrounded the foundational core of Sant Mateu in the high part of the population, in the surroundings of the Church of San Pedro.
The first walled enclosure, from the 18th century, has only a few traces left in the sacristy and in the wall south of the Church of San Pedro. We have references in documents from the Llibre de Privilegis dated from 1237 and 1300 and in the process of the Inquisition against the Cathar Guillem de Belibaste celebrated in Carcassonne in 1321.
From the complex of the mountain wall, from the 14th century, apart from the stretch of canvas parallel to the Palace river also lies some smaller remains of some of the access doors such as the Morella gate and the Cantacorps Tower and of other sections of the wall.
The victory of the House of Bourbon in the War of Succession brought with it the order to demolish the walls of Sant Mateu partially completed during the 18th century. The end of the First Carlist War marked the progressive disappearance of the walled enclosure of Sant Mateu with the destruction of the stretch of wall and its gates whose materials were used in the construction of houses.