I took this picture last July a few minutes after we had taken off from Istanbul. We were flying north (to the left in the picture) over the Black Sea, the land below is Turkey and the narrow channel in the distance towards the east is the Bosphorus that separates Europe from Asia.
Before I examined John Arrowsmith's 1844(?) map of Turkey in Europe (downloaded from the David Rumsey Historical Map Collection), I didn't know that another name for the Bosphorus was the Channel of Constantinople. (In Arrowsmith's map, north is towards the top.)
The Symplegades ("Clashing Rocks"), made famous by Jason and the Argonauts, are assumed to have been located at the northern opening of the Bosphorus (see map here). I believe the Cayennees Islands (a.k.a Cyanean Rocks) marked in Arrowsmith's map are the Symplegades.