The amphitheatre dates from the end of the first century and is located in the lower part of Frosinone near the River Cosa. Although it was mentioned by historians, the amphitheatre was only discovered in 1965 and a part is incorporated in a building of the twentieth century.
The original structure had an elliptical ground plan with a major axis 80 meters long at whose ends were the main entrances. The amphitheatre could hold about 2,000 people and had a single set of steps.
The amphitheatre stood next to an important road with a bridge over the Cosa river and, in its vicinity, there are the remains of the ancient bridge and a fountain. The baroque fountain was built on a former Roman fountain.
A reconstruction of the amphitheatre can be seen in the Archaeological Museum.