The theatre was discovered between the 19th and 20th  centuries during excavation works under the supervision of  the local archaeologist Giuseppe Sordini. It dates back to the end of the 1st century BC.

The building stands on a large artificial platform delimited by a semicircular ambulacrum which leads, through three entrances, to the cavea, on whose steps spectators took their seats.

The orchestra, i.e. the central space intended for the choir, and the pulpit (stage) are also preserved, both embellished with polychrome marble cladding, while the scene behind it, which housed the backdrops for the shows, was greatly altered in the Middle Ages due to of the construction of the church of Sant'Agata.

The visit to the theater continues with the National Archaeological Museum which, since 1985, has been housed in the former monastery of Sant'Agata, built at the end of the 14th century in the area of the Roman theater of Spoleto.
The exhibition halls are located on different levels of the building: on the first floor, finds from the city center and the surrounding area are displayed and go from the city's origins during the Bronze Age (II-I millennium BC) to the Roman era.

The section dedicated to the archaeological interventions carried out on the Sant'Elia hill, the place where the Rocca Albornoziana stands, is of great importance.The materials on display illustrate all the historical phases of the area, from the settlement at the end of the 2nd millennium BC until medieval times.

On the second floor of the museum, finds from the Valnerina valley are on display, an area that in ancient times had important cultural ties with the city of Spoleto. The two memorial stones dating back to the 3rd century BC, known as the "lex luci Spoletina", are also visible in this part of the building.
Laws concerning the protection of sacred woods dedicated to the God Jupiter are inscribed in archaic Latin in the two stones.