This fortress is thought to have been built by the Malaspinas, a Tuscan family who arrived on the island in the mid-11C. The castle occupies 2 000m2 and has a 300m perimeter and seven polygonal and square towers. The church within the castle walls, Nostra Signora de sos Regnos Altos, has a fine series of Provençal Tuscan-style frescoes (1350-1370). The stairs east of the castle lead down to the Sa Costa quarter.