The castle of Monsanto is implanted in a rocky massif, on the right bank of the river Pônsul, the origin of its first foundations is a question still open, thinking that Lusitanians, Romans, Visigothic and Arabs may have contributed.The castle itself, of military and medieval architecture of the templary nature, was ordered to build by D. Afonso Henriques, under the responsibility of D. Gualdim Pais. 

In the reign of D. Dinis it suffered reconstruction and expansion of his defenses. In the reign of D. Manuel I, the castle defenses were strengthened with the building of five towers. He has undergone further remotions during the Restoration War (17th), and was also remodeled atthat time the chapel of N. Sra. of Castelo. During the Peninsular War (beginning of the century. XIX), was again remodeled having been demolished the five towers, and built three new booster batteries to the entrance gate and a collateral bulwark and adaptation of the Castle Church to military Paiol, which later exploded and caused serious damage to the castle.

 

After many transformations and demolitions over the centuries, the castle and the walls of Monsanto were classified in 1948 as a national monument.