The Teatro Romano di Ostia Antica was built in the Augustan age and remodeled at the end of the 2nd century. It was built in the area that in the Republican age had been delimited for public use by the urban praetor of Rome along the Tiber, east of the walls of the republican castrum. In the Augustan phase, it could accommodate 3000 spectators, which became 4000 after the reconstruction.

It was a typical Roman theater, with a caveat supported by arches, overlooking the documents Maximus: the spaces between this and the curvilinear facade of the theater had been paved in travertine and bounded by travertine stones, also equipped with chains, and there were two nymphaeums. semicircular (monumental fountains) ( II, VII, 6-7 ).

In front of the theater on the documents, there were two arches, of which the pairs of brick pillars remain, which leaned against the arches of the theater and the portico of the triumphal arches, on the opposite side of the street. It was the honorary arch dedicated to Caracalla by the citizens of Ostia in 216. Perhaps the two arches were connected by a wooden roof, thus acting as an entrance hall for the theater.

The arches of the façade, extensively restored, rested on massive brick pillars with a travertine plinth. Above this rose the Tuscan pilasters that framed the arches of the first order, with capitals, bases, and entablature made with specially shaped bricks. The façade originally had two orders of arches, surmounted by an attic with windows; at the second-order, the brick pilasters were of the Ionic order and other smaller pilasters were present on the sides of the windows of the attic, perhaps of the Corinthian order. Above the windows of the attic, there were protruding shelves, intended to support the sturdy wooden poles that supported the curtain, inserted in the crowning cornice.

Inside the arches, there was a concentric portico-ambulatory, which gave onto a series of sixteen radially arranged rooms, alternated with the central entrance towards the lower places and the four staircases that allowed to reach the seats at the second and third level. The sixteen radial rooms housed tabernas (shops) equipped with a back room and a mezzanine, reachable by a staircase of which the first stone steps remain. The tabernas were decorated with simple frescoes. In the ambulatory, to the right of the main entrance, there is a well with a travertine puteal.

The central access corridor had marble coverings on the floor and walls and the vault decorated with stucco. In the 4th century reconstruction, marble seats were placed in the innermost part, which reuses bases from the Piazzale Delle Corporation, no longer in use. The outermost part and the adjacent rooms (tavernas with backroom) became cisterns, with the walls covered in signing: from here the water reached the orchestra through two holes made in the sidewalls of the innermost part of the corridor.

Originally the corridor allowed instead to reach the orchestra, which was also originally paved in marble. The first three steps of the cave, low and with marble cladding still preserved, were intended to house the seats for the places reserved for the most important characters. The upper sectors followed and a portico in summa cave (at the top of the cave) with marble columns (today raised out of place behind the scene).

One of these bears the relief of a genius in front of an aedicule, dressed in a cloak holding a cornucopia in his left hand, while with the patera in the right he performs a libation on a cylindrical altar. The inscription below dedicates the relief to the genius of the Castra peregrina by the brothers Optaziano and Pudente, belonging to the military corps of the frumentarii.

The parodoi, corridors between the auditorium and the scenic building, on the sides of the orchestra) retain remains of the original masonry from the Augustan period.

The raised proscenium above the orchestra was decorated on the front with a series of alternately semicircular and rectangular niches, covered in marble and framed by small columns that supported a protruding crown. On top of it there are shelves decorated with theatrical masks, which must have belonged to the decoration of the building in the Severian phase.

The front scene (frons scaenae) was devoid of articulation in niches, taking up the linear plan of that of the Augustan period. Marble pillars and columns leaned against it, arranged in three orders.