The spectator seats are orientated to the South, towards the Ancient city in the lowland and the Rhodope Mountains. In plan, the theatre is a semi-circle with an outer diameter of 82 meters.
The open spectators area – cavea, includes 28 concentric rows of marble seats, divided into two tiers by an aisle - diazoma. The upper part of the tiers is interrupted by narrow radial stairways, which divide the cavea into wedge-shaped sectors – kerkides. The spectator seats surround the stage – the orchestra, which has the shape of a horseshoe and is 26.64 meters in diameter.
The stage building – the skene, is situated south of the orchestra. It has 3 floors. The stage area – proskenion – is 3.16 meters high and its facade, which is facing the orchestra, is decorated with an Ionic marble colonnade with triangular pediments.
The facade of the skene which overlooks the spectators area consists of two 2-storey porticos – the first storey is treated in keeping with the Roman Ionic order and the second – with the Roman-Corinthian order. The facade is cut through by three symmetrically located gates.
The entrances to the orchestra - parodoses - which were initially uncovered and, afterwards vaulted, connect the cavea with the stage building. An underground vaulted passage begins from the centre of the orchestra, goes under the stage building and leads out of the theatre.
Another vaulted passage, passing under the central bank of seats of the top tier, connects the cavea of the theatre with the Three Hills area. Over the passage the box of the dignitaries was situated.
According to a builders’ inscription, discovered on the frieze-architrave of the eastern proskenion, the construction of the theatre dates back to the time of Emperor Trajan.
Similar to all the theatres on the territory of the Roman Empire, in the theatre of Philippopolis the honorary spectator seats were inscribed. There were inscriptions not only for the representatives of the city council but also for magistrates, friends of the Emperor, etc. Some honorary inscriptions show that the building was used as the seat of the Thracian provincial assembly.
Presumably, some of the fights with animals were held in the theatre, as remains of safety facilities in front of the first row are uncovered. These additions were set because of the visit of Emperor Caracalla to Philippopolis in 214 AD.
The restoration of the Roman Theater in Plovdiv is considered one of the best achievements of the Bulgarian Conservation School. The intervention is limited on the basis of rigorous tests and exclusion of assumptions. The reconstruction was made strictly according to the method of аnastylosis and the new material is clearly visible. Today the theater of the Three Hills is one of the emblems of the city and a stage for classical drama, dance and music.