Construction of Arab origin was terminated by the Normans, who made it a royal residence in 1072. Of the original four towers survive today only the Pisan used the 700 as an astronomical observatory, several rooms inside including the beautiful "Sala d'Ercole" painted in 1799 by the Sicilian Regional Assembly seat Velasquez, the hall of King Roger rich golden mosaics, the yellow room full of frescoes, the room with the paintings of the viceroy viceroy in Sicily. Under Frederick II the building reached its zenith and became the center of culture of his reign. A defense of the building the bastion of St. Peter, built between 1550 and 1560 and later converted into a hanging garden with many exotic plants inside.