This castle can also be reached from the road that leads from Cassino to Montecassino. The fortification, which dominates the city from a steep cliff (193 m above sea level), was built around the middle of the 10th century by the abbot of Montecassino Aligerno, to defend the abbey.
Rocca Janula, toponym for "small door", or "protector of the doors" according to another reading, was built by the will of the Abbot Aligerno in the 10th century, to allow a 360 degree defense.