It is the most important monument of military architecture in the municipality. The exact date of its construction is not known, but it is thought to date from before the 1209 charter of Afonso IX of León. The fortification has undergone many alterations over the years and it was after the reforms of King Dinis that the castle was surrounded by a barbican, which meant that access to the inside of the fortress had to be made via an enclosed route. King Manuel I ordered the restoration of the walls again after some years, and it was only in 1922 that this monument was recognised as a National Monument. It underwent its final restoration in 1940.

It is an old village of marked medieval features and is composed of two very distinct nuclei: the old village, of original foundation, composed of a castle, a church in ruins and traces of medieval town planning, all of them surrounded by a 12th century wall; and the new village, or Arrabalde de S. Pedro, protected by a wall built during the reign of D. Dinis, of marked gothic characteristics, and strongly affected by the 1755 earthquake.

This tower is the most relevant physical memory of the passage of kings in the city, as well as of the defence of the kingdom against Castile. The interior has three floors with wooden floors, each one with a different experience. On the ground floor there is an auditorium where a film is projected that promotes a virtual tour of the city. On the Livro Mágico floor (2nd floor) visitors can browse the History of Guarda in an interactive way, through the Carta de Foral and the cartoon "História da Guarda Oitocentos Anos de Cidade". On the top floor they can have a 360º perspective of fantastic landscapes.