Hellespont

The Hellespont was a body of water on Earth.

The city of Byzantium, later known as Constantinople and Istanbul, was usually approached from the Aegean Sea, after which ships would pass through the Hellespont and the Sea of Mamara before arriving at the city. (PROSE: Byzantium!)

Behind the scenes
The Hellespont is classical name for the strait which lies between the Aegean Sea and the Sea of Mamara. In the modern day it is known as the Dardanelles or the Strait of Gallipoli.