With Islamic occupation between the 8th and 12th centuries, the Castle of Palmela was conquered by D. Afonso Henriques, in 1147 and definitively recovered by D. Sancho I. Definitive seat of the Order of Santiago, from 1443 until its extinction, in 1834, the fortification has been a National Monument since 1910.

The geographical position of the castle allows a strategic domain of part of the Sadian estuary, a side of the Arrábida mountain range and the surrounding plains that separate it from the Tagus. This situation, in other times, was of utmost importance due to the connections and communication possibilities established with the castles surrounding the Tagus and Sado lines.

Within the walls of the Castle are: the Pousada Histórica de Palmela, located in the former convent of the Order of Santiago; the Church of Santiago; the ruins of the Church of Sta. Maria, in whose sacristy the Study Office on the Order of Santiago is housed; the Tourism Office; craft shops and regional products and a Café-Espanada.