A stage wall was added during the reign of the Roman emperor Domitian (81-96). At the same time, a low wall was built, surrounding the orchestra (the semicircular space in front of the stage); this suggests that the theater was now also used for gladiatorial contests. .
In 365, Apollonia suffered heavily from a big tidal wave, and the theater was suddenly a lot closer to the sea. The noise of the waves must have made normal performance impossible, and the stage wall was demolished in the fifth century, to reuse the columns in the Eastern Basilica.
In the background of the photo, you can see the remains of an immense mole that closed the eastern harbor.