Amid the scant ruins of Seleuceia in Pieria, is this this astonishing feat of Roman engineering. From the ticket kiosk, follow the trail along an irrigation canal and past some rock shelters, finally arriving at a Roman arch spanning the gorge and the tunnel entrance. Bring a torch as the path can be slippery. At the far end of the channel an inscription provides a date for the work carried out by sailors and prisoners from Judea.
Seleucia lived under the constant threat of flooding from a stream that descended from the mountains and flowed through the town. To counter this threat, 1st-century Roman emperors Titus and Vespasian ordered that this 1.4km-long channel be cut through the solid rock to divert the stream.
About 100m from the tunnel are a dozen Roman rock tombs with reliefs, including the excellent Beşikli Mağarası (Cave with a Crib).
The tunnel and remnants of Seleuceia, Antioch's port in ancient times, are in the village of Çevlik, 5km northwest of Samandağ.