Dating back to the end of the tenth century, it belonged to Aquino counts and between 1244 and 1245 St. Thomas Aquinas was imprisoned there. Because of its strategic position, it has played for centuries the function of defending the southern borders of Papal State. It was destroyed by the troops of Charles VIII in 1495 and suffered serious damage in the earthquakes of 1703 and 1915, which forced to demolish the upper floors. After the restoration, it includes the ducal palace, with the underground jails and the rooms where St. Thomas was held prisoner; an appellation, a square-shaped male tower and a pentagonal tower. A Renaissance palace with a fountain in front of the entrance was added to the actual castle.