This strong castle, located in a remarkable site which was already inhabited in Roman times, was built in 1135 by the first .King of Portugal, Afonso Henriques, to defend the south border of his kingdom when Santarém and Lisbon were under Moorish domination. After the sacking of these towns in 1147, the castle lost its importance. In the 14C, King Dinis had it rebuilt to live there with his wife, Queen Isabel.