The ducal castle was built before the year one thousand, it could hold more than a thousand soldiers and it was one of the most efficient and impregnable fortresses in the centre of Italy. It was not able anyway to hold the attack of the king of France, Charles VIII in 1495. St.Thomas Aquinas was imprisoned in the castle (1240-1242). Today, the castle includes a very high level restaurant: Corte d'Avalos.