According to inscriptions on the entrance, this tunnel was started in 69AD when Vespasianus was in power, and completed under the rule of his successor Titus in 81AD.
It was designed to divert water flows which threatened to silt up the harbour and only the first 100 yards or so are a true tunnel, after that it is a deep cutting in the rock.
It was all hewn by Jewish slaves banished to what was then Seleucia Pieria, a huge city destroyed by earthquakes in the sixth century and now long buried.
Seleucia Pieria has never been excavated and its ruins are scattered around the modern seaside village of Çevlik.
All of this we learned from our guide book as we never actually reached the tunnel.
The only way into the tunnel these days involves walking up the cutting from the beach end and, on the day we tried, it had been raining hard for several hours and the cutting had turned into a mini Saklıkent Gorge.
Except this had sheer walls where the rock had been hewn away. We did try to make our way up on the edges of the water but, inevitably, one of us fell in and we abandoned the attempt to reach the tunnel.
In fact it is clearly a place that should only be visited in summer when the bottom will be bone dry.
Keen readers who would like to see the tunnel can ‘Google’ it.
We squelched on to visit the local necropolis which didn’t disappoint – but that is another article.