The Thorikos Theatre is the oldest known theatre in existence. Located north of Lavrion, almost adjacent to the city, it dates from the end of the Archaic era, between 525 and 480 BC. Unlike Greek theatres of later eras, it is elliptical rather than circular in shape and has a rectangular, rather than circular, orchestra.

With 21 rows of seats, the theatre had a capacity of 4,000. On the east side of the orchestra is the base of the ancient temple and a room with benches, all sculpted out of the indigenous stone.

Dating from the mid-fifth century, the temple was also used for official meetings of the local citizens. The stage was made of wood, not replaced with stone like those of later theatres.