Built on the top of a steep hill in the old part of the town, the Castle of Mértola, with a walled enclosure of approximately 3,000 m2, was during the 14th century the national headquarters of the Order of Santiago.
After entering through a door where one notices the reuse of another one from the Islamic period, and after an elbow-shaped passage, we enter an old weapons square where a rectangular cistern stands out. To the north stands, dominant and monumental, the Keep. Above the door, in an inscription of the time, one can read: “The construction of this tower was ordered by Dom João Fernandes, the first master (of the Order of Santiago) there was in Portugal. It was from 1330" (1292).
During an initial archaeological intervention in the castle, it was found that the interior of the fortified enclosure, before being militarized, was occupied in the Islamic period (11th century) by a housing neighbourhood.
