The Castle of Marvão was a strategic detention fortification, oriented towards the border, which is a mere 13 km away. It also constituted an effective place of refuge and an extraordinary point of observation and surveillance, since it clearly dominated the second most important route of penetration of the armies of the neighboring country, from Valencia de Alcântara, in a vast area of the Alto Alentejo that goes from Badajoz to the Tagus river. Its strategic insertion is clear: it is part of the first detention line, after the Treaty of Alcanizes, which runs, in the current District of Portalegre, from Montalvão to Elvas. The most rocky of the national castles, it is constituted in two contiguous enclosures that, for defensive reasons, had to include all the highest rocky crest.