Casinum was an ancient town of Italy, probably of Volscian origin. Varro states that the name was Sabine, and meant forum vetus, and also that the town itself was Samnite, but he is probably wrong. When it came under Roman supremacy is not known, but it probably received the citizenship in 188 BC. It was the most southeasterly town in Latium adiectum, situated on the Via Latina about 40 miles north-west of Capua. It appears occasionally in the history of the Hannibalic War. Varro possessed a villa near it, in which later on Mark Antony held his orgies.
Towards the end of the republic it was a praefectura, and under the empire it appears as a colony (perhaps founded by the triumvirs), though in two (not local) inscriptions it is called municipium. Strabo speaks of it as an important town; Varro mentions the olive oil of its district as especially good. The older Volscian Casinum must have stood on the hill (1,715 ft) above the Roman town (148 ft), where considerable remains of fortifications in Cyclopean masonry, of finely cut blocks of limestone, still exist.
The site is now occupied by the Benedictine monastery of Monte Cassino founded by St. Benedict himself in 529. A number of Roman inscriptions from Casinum are preserved there. The wall which runs southwest and west starting from the west side of the monastery, for a total length of about 300 yd., is not so clearly traceable on the other side of the hill, though there is one fragment under the east side of the monastery; but it seems to have defended the summit and was perhaps the original acropolis.