There is unfortunately not much left to see of what used to be the Amphitheatrum Castrense in Rome. The ruins of this amphitheater can be found at the Via Nola, between the Aurelian Walls and the Basilica of Santa Croce in Gerusalemme.
Amphitheatrum Castrense Rome
Address, opening hours and admission
Address: Via Nola, snc – Rome. Opening hours: The site can only be visited on the first and the third Saturday of the month. Booking is mandatory: +39 06 39967700. Admission: 5,50 Euro; children 0-11: Free. There is a 2 Euro booking fee. The tour is part of a visit to the Palazzo Sessoriano (see below).
History and description

The Anfiteatro Castrense is supposed to have been commissioned by the Emperor Elagabalo, who reigned from 218 until 222 AD. It was probably meant to be the amphitheatre of the imperial palace. The word castrum originally meant “(army) camp”, but later came to signify “imperial dwelling”.
The amphitheatre was part of a building complex that was known as the Palazzo Sessoriano. Other buildings part of this villa were the Circo Variano and the Terme Eleniane.
The complex was constructed between the end of the 2nd and the beginning of the 3rd century. It was mostly used for military manueuvers honouring the imperial court and for spectacles.
The reason it is preserved better than expected is that it was incorporated in the Aurelian Walls. A great part of what is left is found below the present day street level, however.
The monument has an elliptical shape of 88 by 76 meters. Most of the material used is a Roman brick called laterizia. In some spaces travertine marble was used.
It consisted of two rows of arches. The openings of the first row were framed by Corinthian half columns, while those of the second row were divided by pillars. Renaissance drawings show that there was also a third wall, with windows and supports for the beams that held the velarium (a sheet that protected the audience from the sun).
There used to be a long (300 meters) and wide (14,50 meters) covered hallway between the amphitheatre and the Circo Variano. It ran alongside the great hall that was later transformed into the Santa Croce in Gerusalemme Church. Ruins of both the hallway and the circus can be seen behind the church.