The ancient theatre at Delphi was built further up the hill from the Temple of Apollo giving spectators a view of the entire sanctuary and the valley below.

It was originally built in the 4th century BCE but was remodelled on several occasions, particularly in 160/159 BCE at the expense of king Eumenes II of Pergamon and in 67 CE on the occasion of Emperor Nero's visit.

The koilon leans against the natural slope of the mountain whereas its eastern part overrides a little torrent that led the water of the fountain Cassotis right underneath the temple of Apollo.

The orchestra was initially a full circle with a diameter measuring 7 meters.

The rectangular scene building ended up in two arched openings, of which the foundations are preserved today.

Access to the theatre was possible through the parodoi, i.e. the side corridors. On the support walls of the parodoi are engraved large numbers of manumission inscriptions recording fictitious sales of the slaves to the god.

The koilon was divided horizontally into two zones via a corridor called diazoma. The lower zone had 27 rows of seats and the upper one only 8. Six radially arranged stairs divided the lower part of the koilon into seven tiers. The theatre could accommodate about 4,500 spectators.