The largest theatre in the ancient world, with a seating capacity of about 25,000, built into the natural slope of Mount Panayır. Originally constructed in the Hellenistic period under Lysimachus, it was substantially rebuilt and enlarged under successive Roman emperors from Augustus through Trajan. The three-storey stage building, largely collapsed, would have risen to roughly the height of the cavea and created an enclosed acoustic environment.
The theatre looks down the full length of the Arcadian Way — the marble-paved ceremonial street, once lined with columns and statues, that ran from the theatre to the ancient harbour. Today the harbour has silted up entirely and the view ends in farmland, but the orientation makes the urban logic of ancient Ephesus immediately readable. Concerts and events are occasionally staged in the theatre in summer; the acoustics remain excellent.