Declared Heritage of Cultural Interest, the only preserved section of the town walls measures 260 m and falls on the right edge of the Palace River. It was restored in 1996. The Montesian town walls which surrounded Sant Mateu had a perimeter of 1,600 m and eight entrance gates. The building’s masonry has a variable thickness and a height of 6 m, including the battlements. It is about the second walled enclosure in Sant Mateu. It was built from 1357 to 1380 in the leadership of Pedro de Thous. It replaced the first wall from the 13th century, which encircled the founding centre of Sant Mateu situated at the top of the town, in the surroundings of St. Peter’s Church.
Nowadays, from the first walled enclosure (13th century), there are only some traces in the sacristy and in the southern wall of St Peter’s Church. We also have reports about it in the documents of Llibre de Privilegis (cartulary) dated to 1237 and 1300 and in the inquisitorial system against the Cathar Guillaume Bélibaste, held in Carcassonne in 1321.