Dominating the landscape of this Alentejo area, with its donjon, the Beja Fortress has the main features of the Portuguese fortifications, yet it is supposed that its origins date back to the Roman occupancy period, being modified and increased all over the centuries.

After some attempts to conquest this town from the Moors, by the first Portuguese king, D. Afonso Henriques, only in 1162 Fernão Gonçalves conquest it, to be again recovered by the Moors. Only in 1200 the town is finally conquered back definitely by the Portuguese crown. In 1254 the town is reconstructed, as it was quite destroyed and depopulated.
Beja was under Moorish domination since 715 and was attacked many times by the Peninsula kingdoms, resisting always until the last Portuguese conquest.

The donjon construction was ordered by king D. Dinis (1279 to 1325) in 1310, and is nowadays considered to be one of the best examples of the medieval architecture. The donjon has about 40 meters high and the access stairway has about 198 steps. Apart the fact that it is considered to be the highest one in all the Iberian Peninsula, it also has the particularity to have been all built in marble.

As other medieval towns, Beja also had a defensive wall structure that protected all the urban area. It had seven main doors, named as Évora, Aviz, Mértola, Aljustrel, Moura, São Sisenando and Corredoura.

Also quite interesting is the alcazaba, situated in the Arms Square, that was built by king D. João II in 1485 to house the Infants D. Isabel of Castile and D. Afonso of Portugal, considered to have a big heritage and architectonic value.