Sluice gate?

The corridor in between the foundation of the stage (pulpitum / podium) and the seats (cavea) in
this Roman theater, is called aditus (approach, access). On both sides of the Roman theater of
Caesarea the aditus could be blocked by a double set of wooden boards, in use for a naumachia,
a Roman sham battle on an artificial lake, in this case inside the theater.