In the village of Amieira do Tejo, in the municipality of Nisa, in Portalegre, the Amieira Castle is an excellent example of 14th-century military architecture. By order of the Prior of the Order of the Hospital, D. Frei Álvaro Gonçalves Pereira, it was built in 1350. It consists of a quadrangle flanked by four square towers. Of all the castles in Alentejo, this one was involved in a single military episode. In 1140, Princess D. Leonor had a disagreement with Prince D. Pedro and left to Crato with D. Nuno de Góis. The forces of Castile were invoked by D. Nuno and Amieira was besieged. In the face of this episode, Pedro ordered the occupation of the castles of the priory of Hospital in Crato. In the end, the castles surrendered and the prior of Crato and Princess D. Leonor fled to Castile, and peace returned to Amieira. In the following centuries, it underwent modernisation works, since part of the building was already in ruins. The Amieira Castle has been classified as a National Monument since 1922.