Shorter and generally narrower and swifter-flowing than the Hellespont, the Bosporus ranges in width from 2.5 miles to 400 yards. Its name, “cow ford” or “ox ford,” was in ancient times said to refer to the mythical wanderings of IO, a woman loved by the god ZEUS and transformed into cow by Zeus’s jealous wife, HERA. But the name may refer to a more mundane cattle crossing.
Around 513 B.C.E., the Persians under King DARIUS (1)—preparing to cross from Asia to Europe for their invasion of Scythia—spanned the Bosporus with a pontoon bridge consisting of about 200 ships anchored in a row. This was a remarkable engineering feat in the ancient world, although not as amazing as the Persians’ bridging of the Hellespont, a wider channel, 30 years later. In modern times the Bosporus, now a part of Turkey, was not bridged until 1973.
The Bosporus and Hellespont were the two bottlenecks along the shipping route between the Black Sea and the Aegean. This route had become crucial by about 500 B.C.E. when ATHENS and other cities of mainland Greece were becoming dependent on grain imported from the northern Black Sea coast. As a natural site where shipping could be raided or tolled, the Bosporus, like the Hellespont, offered wealth and power to any state that could control it. This, combined with the excellent commercial fishing in the strait and its value as a ferry point, helps to explain the prosperity of the Bosporus’s most famous city, BYZANTIUM, located at the southern mouth. Athens controlled the Bosporus in the 400s B.C.E. by holding Byzantium as a subject ally.
Further reading: John Freely, The Bosphorus (Istanbul: Redhouse Press, 1993); Yusuf Mardin, Bosphorus Through the Ages (Ankara: T. C. Kültür Bakanligi, 1995); Rhonda Vander Sluis, From the Bosphorus: A Self-guided Tour (Istanbul: Çitlembik, 2000).