At the foot of the stage box two corridors allowed the passage of the actors, back-drops and scenes. Behind the construction, closing the stage, were located some little cubicles with barrel vaults entirely covered by white marble, to be interpreted as dressing-rooms for actors.

The exterior facade of the stage was embellished by a colonnade supporting a long porch which exceeded the stage itself. All the remaining external front of the theatre was decorated by a series of round barrel-vaults supported by pillars adorned with half-columns. Both the pillars and the half-columns were made of bricks and tiles and this kind of architectural example was evidently executed with an extreme mastery, both for the regularity of the joints and for the constant repetition of the building technique and, most of all, for the cut and smoothness of the small bricks forming the half-columns. However, the regular holes of the cramps prove that in spite of such precision, even the external front was covered by marble slabs. The whole theatre building, embellished by numberless arcades and by shining marble slabs, was lifted and exalted as a contrast on a high base of great parallelepipeds in volcanic stone which, as a podium, insured a solid static expedient in addition to a certain chromatic effect. The porch built behind the stage originally had eight columns. Afterwards, the last two columns of every side were incorporated into two small rooms, in this way reducing their number to fourteen. Today some bases of these columns are still visible. The grey ones, which were made of the same volcanic stone of  low podium and were at the front, were probably not stuccoed and, as often happened in the ancient world, they were made with material of little value, just to emphasise, in this case, the chromatic effect we were talking about before. If the columns were stuccoed, they were also painted in artificial dark marble, similar to the grey stone of the base, on which the whole edifice and the porch itself rested. We know that the arcade was explicitly destined to protect the spectators from sudden rain and to offer them a shady place during the summer heat or, in any case, it was a place for walking and conversation. The study of the walls gives the construction of the theatre to be half-way through the first century AD, while the added rooms and some little restoration can be dated between the end of the first century and the first decade of the second century AD. Its quite reduced dimension and the richness of its marbles did not make the theatre very popular but rather destined it, from the Imperial Julia Claudia family which built it, for the elegant and refined society that used to crowd Antium, mostly during the summer time.