Hello!
Lucky for you I know the answer!
By the 5th century BC, theatre had become formalized and was a major part of Athenian culture and civic pride, and this century is normally regarded as the Golden Age of Greek drama. The centerpiece of the annual Dionysia was a competition between three playwrights at the Theatre of Dionysus.
So it was around 5th century B.C.
Hope this helps!
~COurtney