The Roman theater is the main preserved public building of the ancient Teanum Sidicinum, today Teano. It is a grandiose theatre-temple, located in the locality of Grotte, probably dedicated to Apollo, as can be deduced from an epigraph in Oscan on a limestone altar table, where a local magistrate gives to the aforesaid divinity.

The building was built at the end of the 2nd century BC. in uncertain work and blocks of tufa, and it is the oldest theater in Italy entirely supported by radial walls and rampant vaults.

The theater was later enlarged in considerably monumental forms under the reign of Septimius Severus at the end of the 2nd century AD. The enlargement of the theater auditorium dates back to this second phase, reaching a diameter of 85 m, as well as the complete refurbishment of the grandiose scenic building in which columns and trabeations of large dimensions were used and rare and precious marbles were used and many sculptures, some of reuse of the Augustan age.