Amid the scant ruins of Seleuceia in Pieria at Çevlik, 5km northwest of Samandağ, 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. 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 Vespasian and then Titus ordered that this 1380m-long channel be cut through the solid rock to divert the stream. Some 130m of the tunnel is closed and the rest open.
About 100m from the tunnel is the curious Beşikli Mağarası (Cradle Cave) with almost 100 Roman rock tombs with scallop-shaped reliefs.
Dolmuşes run between Antakya and Samandağ (₺10, 40 minutes, 28km), where you can change for another bound for Çevlik (₺3, 15 minutes).