Keep and first shirt

The keep or tower of San Miguel, the centre of the present-day castle, was designed and built in the second half of the 10th century as an isolated tower with a rectangular ground plan. At its base are large, elongated ashlars (reaching a height of more than a metre), arranged in a rope-and-tenon pattern (alternating longitudinal and transversal positions), which is present in contemporary buildings in other areas of Christian Spain (Aragon, Soria), but which corresponds to Muslim construction techniques. The tower, which was around 20 metres high, had up to four levels above the rocky ground, articulated by means of Structures made of wood. Access was not via the ground floor ( leave), but through a doorway on the third level, which was reached by a ladder. The thickness of the wall decreased as the height increased. The tower was halved in 1516 and rebuilt in the mid-20th century.

In the 11th century, a shirt-shaped construction enveloped the keep on three of its flanks, leaving only its north flank uncovered. On the ground floor, leave , there are two rooms. To the west is the chapel of San Miguel, considered the patron saint of the castle, represented by a polychrome carving from the 18th century. At his feet hangs a copy of Velázquez's Crucified Christ.

On the east side is a room called the Saint's Room, because according to a family tradition of the Counts of Xavier (not attested to before the 19th century), Saint Francis Xavier lived there before his departure for the University of Paris (1525). It has two canvases of the saint from the second half of the 17th century and another of the Virgin and Child from an earlier century.