The fortress or Montpalau castle was built during the 15th century, when the Montpalau family decided to leave Santa Magdalena castle, located on the right side of the river Fluvià very close to the present village of Sant Jaume de Llierca, and moved to the centre of the village. They lived there until the 17th century. It is a great example of a Catalan Gothic castle-palace. On the main façade there is a large Gothic window and three stone emblems. The one in the midde corresponds to the Montpalau family and the rest correspond to other related lineages. The Montpalau family lived in Argelaguer's castle-palace until the 17th century, when they moved to Barcelona. Nowadays, in the centre of Argelaguer, there are still some remains of the old castle walls in areas such as the Muralla Street. Only two of the three parts have been documented: the first section is parallel with the creek and is 3,4 metres high. The second one is parallel with the Muralla Street and is 3 metres high. It is also known that the castle had a moat, although there are no remains left.