After successive occupation by Celts, Romans and Muslims, the town of Campo Maior was reconquered in 1230, definitively integrating the Portuguese territory with the Treaty of Alcanices (1297). The castle was built a few years later, in 1310, by King Denis of Portugal at the same time as a charter letter was granted to the town. It was built at the top of the Outeiro de Santa Vitória, at 299 m altitude, in the middle of the raia, 10 km from the border line and 18 km from Badajoz and Elvas (places that can be seen from its towers).
At the end of the 15th century, due to the strategic importance of Campo Maior in border defence, King John II of Portugal ordered the construction of a new set of walls to cover the entire urban perimeter, which had expanded considerably in about 200 years.
After the Restoration of Independence in 1640, the country's entire defensive system was strengthened, with the construction of large fortified ensembles, such as Elvas, or the reconstruction and expansion of old castles and forts. In this context, in 1645, by order of King John IV of Portugal, work began on the construction of the bastion fort of the Castle of Campo Maior, under the guidance of João Cosmander, succeeded in this position by Nicolau de Langres.
In the middle of the 18th century, after a violent storm and a fire significantly damaged the castle, King John V of Portugal ordered its reconstruction, transforming the ancient medieval ruins into a smaller but more operational fort. The Chapel of Senhor dos Aflitos was also built inside the castle fence in the 18th century.
