Montesarchio (Latin: Caudium; Greek: Καύδιον) is a comune in the Province of Benevento, Campania, southern Italy. It is located 18 kilometres (11 miles) south-east of Benevento in the Valle Caudina at the foot of Monte Taburno. The commune was granted the official status of City (Città) by a presidential decree of 31 July 1977.
Montesarchio is the site of ancient Caudium, an ancient city of Apulia et Calabria, situated on the road from Beneventum (modern Benevento) to Capua. It seems probable that it was in early times a place of importance, and the capital or chief city of the tribe called the Caudini; but it bears only a secondary place in history. It is first mentioned during the Second Samnite War, 321 BCE, when the Samnite army under Gaius Pontius encamped there, previous to the great disaster of the Romans in the neighbouring pass known as the Caudine Forks; and again, a few years later, as the headquarters occupied by the Samnites, with a view of being at hand to watch the movements of the Campanians. The town of Caudium is not mentioned during the Second Punic War, though the tribe of the Caudini is repeatedly alluded to.