The formerly classical Greek theater was expanded by the Romans with additional tiers of spectators (cavea) in a 180° arc, slightly larger than a semicircle, and provided with a circular stage (orchestra) for performances.
The site had already been chosen by the Greeks to take advantage of the natural gradient of a local hillside, which was often rewarded with a wonderful view of the landscape.
During the heyday of Greek tragedies and comedies (5th century BC), a raised stage (scenae) was initially built, initially made of wood, which was later replaced by stone in the Hellenistic era.
The Romans preferred to completely enclose the theater with an additional inner wall, which was also built behind the stage, but which retained the Greek form of the tiers. The side entrances (parodos) were never roofed in the Greek era; the Romans combined the entire structure into a large building complex with covered entrances. If there were no natural slopes for the cavea, they were built on an artificial elevation, e.g., in the form of archways. The rows of benches were usually separated by a horizontal corridor (diazoma).
Source:
alaturka.info/de/tuerkei/tuerkische-riviera/side-manavgat/355-theater-von-side