In July 2003, under the concession of the superintendency, excavation was undertaken of the castle known as the “Castellaccio” or “Castello di Ariscola”. The site is situated at the foot of Monte San Franco (2112 m a.s.l.) near the Valico delle Capannelle (1320 m a.s.l) in the territory of Arischia. The excavation’s aim was to acquire data relating to the spatial organisation of the structure, dating evidence and evidence of the material culture, since the documentary sources regarding the site are scarce or non-existent. The castle, the only “Pass Castle” identified in the area, is situated at circa 1400 m a.s.l. on the summit of a hill from which it dominates the surrounding plain. The keep was polygonal in shape, circa 75 m long on its north-south axis and circa 18 m wide (east-west), with a narrowing to the north, probably the site of a corner tower. On the southern part of the hill was a circular flat space, probably a courtyard, a hypothesis supported by the presence of only one entrance to the structure. Only the western perimeter wall, circa 70 m long, and part of the northern wall, circa 3 m, were preserved for their entire length. There were no remaining traces of the walls to the east and south. East of the keep the hill sloped gently down until there was a drop in height. The space and traces of dwellings, although faint, suggest that the area, once walled, was the site of the castle settlement. The surviving walls, between 90 and 100 cm, were constituted by limestone rough-hewn blocks, from nearby quarries, bonded with white mortar of a medium consistency and with scarce inclusions. Preliminary dating based on the number of finds recovered during the excavation, although limited, places the site within a fairly wide chronological span which runs from the 11th century until the 16th-17th century.