The Main Tower, prismatic in plan, rising to 17 meters high (some added during its reconstruction), is divided internally into three floors topped by a terrace and crowned by square merlons. Ordered to execute on the foundations of a previous tower by D. Dinis in 1324, a gothic epigraphic gravestone, with the royal coat of arms inscribed, indicates this on the left side next to the door. The tower and its enclosure constituted the last stronghold of the military garrison fixed in the Castle. It was used as a royal prison since the middle of the 14th century, and was still active in the second half of the 18th century. In the enclosure, ruined remains of 15th century works persist. Currently, there is a museum center inside.