The castle of Rocca d’Arce was important and impregnable because it was virtually inaccessible due to the nature of the site and important for its “key” geographical position in the conflicts between the Byzantine Empire, the Normans, the Holy Roman Empire, the Papacy, the Guelphs and Ghibellines, and between the various castle lords, dukes, counts and abbots of central Italy.
The castle overlooking the wide valley of the Liri and Sacco rivers. The Sacco valley was called the Tolero in the Middle Ages and Trerus in Roman times, and it was the most important passage between the North and the South of the Peninsula.
The north side is on a precipice of a couple of hundred meters, a limestone cliff with smooth and vertical walls. To the east the cliff was connected to a series of stacks by means of a special wall. To the south and west the ascent to the Castle was prevented by a network of fortifications.