The Bosphorus - Strolling Through Istanbul: The Classic Guide to the City - page 435

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he Bosphorus
We will begin our final tour of Istanbul where we began our first, at the
Galata Bridge, where we will board a ferry to sail up the Bosphorus.
Here we have saved the best for last, for the Bosphorus and its shores
are by far the most beautiful part of Istanbul.
The history of the Bosphorus begins with the “Inachean daughter,
beloved of Zeus” Io, who was turned into a heifer to conceal her
from Hera. Pursued by the jealous Hera's gadfly, Io plunged into
the waters that separate Europe from Asia and bequeathed them the
name by which they have ever since been known, Bosphorus, or Ford
of the Cow. The next event in Bosphoric history is the passage of the
Argonauts on their way to seek the Golden Fleece in Colchis at the
far end of the Black Sea. On our own journey up the Bosphorus we
will stop at several places which ancient and local tradition associated
with Jason and his fabulous crew.
The first fully historic event connected with the Bosphorus is
the passage across it in 512 B.C. of the huge army which Darius
led against the Scythians. From that time onward it played an
important and even decisive role in the history of the city erected at
its southern extremity in 667 B.C.; for, as Gyllius eloquently points
out, the Bosphorus is “the first creator of Byzantium greater and more
important than Byzas, the founder of the City.” And he later sums up
the predominant importance of this “Strait that Purpasses all straits”
by the epigram: “The Bosphorus with one key opens and closes two
worlds, two seas.”
The Bosphorus is a strait some 30 kilometres long, running in the
general direction north-north-east to south-south-west, and varying
greatly in width from about 700 metres at its narrowest to over 3.5
kilometres at its widest. Its average depth at the centre of the channel
is between 50 and 75 metres, but at one point it reaches a depth of
over 100 metres. The predominant surface current flows at a rate of