The theatre we see nowadays stems from a Roman adaptation under Emperor Trajanus, about 100 AD, of the earlier Greek theatre. It housed 25000 spectators, and half of it is built into a hill. The higher parts have been built up.
The stage building used to have three floors and was decorated like a palace facade with marble in several colours, columns and statues. From there actors could reach the proscenium from three entrances. Only the lower floor remains. The front was 140 meters wide, the theatre would rise ten meters higher than the present 30 meters.
On one side of the theatre upper part there are the remains of a late Byzantine castle (maybe 7th century), later changed by the Seljuks.