It was built in the middle of the twelfth century, frequently restored until 18th -century interventions. This mighty building stands on a garden surrounded by baroque style walls; two towers with double lancet window and impressive 16th-century portal with Gothic figures dominate it. The Norman apsidal front shows geometric and animal patterns of great value. The severe lines of the interior belong to the late 18th-century. In the chapel on the right you can find the imperial tombs of Frederick II, his wife Constance of Aragon, Roger II and his daughter, the empress Constance. The silver cinerary urn containing the relics of the patroness Santa Rosalia is kept in the interior.