Casilinum (kăsĭlĪˈnəm) [key], ancient town, Campania, S Italy, 18 mi (29 km) N of present-day Naples. It probably was founded (c.600 B.C.) by the Etruscans. It was captured (215 B.C.) from Carthage by the Romans and served as a base of operations against Capua. Under the Romans it was an important military station controlling the bridge of the Appian Way over the Volturno River. It seems to have been united with Capua by the middle of the 1st cent. A.D. It was destroyed by the Saracens in the 9th cent. A.D.