The Bosphorus, Istanbul, Turkey

Last Updated on December 11, 2022

The Bosphorus is the 32 km (20-mile)-long north-south strait that joins the Sea of Marmara with the Black Sea in Istanbul, and separates the continents of Europe and Asia.

Today, the way to enjoy the Bosphorus is to take a cruise by Dentur Avrasya boatTurYol boat, or traditional Şehir Hatları ferry, a self-guided tour of the European shore, or to relax at a tea-house or restaurant along its shores. You can enjoy a Bosphorus cruise north toward the Black Sea in less than 90 minutes, or in a few hours, or all day, as you wish. More...

About the Bosphorus

Traditionally called Boğaziçi (boh-AHZ-ee-chee, "Within the Strait"), more recently it's been called the Istanbul Boğazı, Istanbul Strait, perhaps to differentiate it from the Dardanelles (Hellespont), called the ÇanakkaleBoğazı.


Ottoman-era Embassy on the Bosphorus, Istanbul, Turkey

An Ottoman-era summer embassym on the Bosphorus.

The width of the Bosphorus varies from 500 meters (1640 feet) to 3 km (2 miles), its depth from 50 to 120 meters (164 to 394 feet), averaging about 60 meters (197 feet) deep.

It runs right through the heart of Istanbul, past the Istanbul Modern Art Museum, several Ottoman palaces, at least two fortresses, forested hills, and shore villages with Ottoman architecture. (For self-guided touring, I've divided it into the Southern Bosphorus and Northern Bosphorus.)

It is crossed by three bridges and a rail tunnel: the southernmost Bosphorus Bridge (Boğaziçi Köprüsü), the central Mehmet the Conqueror Bridge (Fatih Köprüsü), by the MarmarayRailroad Tunnel, and by the Yavuz Selim Bridge at the Bosphorus's northern-end confluence with the Black Sea (2016).

The Bosphorus is one of the world's busiest commercial shipping channels, with some 140 cargo vessels making the 90-minute passage each day (at 7 or 8 knots), carefully navigating the seven precise turns necessary to follow the Bosphorus's narrow channels and avoid its treacherous currents.

Even though by law there are two highly experienced local pilots aboard each vessel during passage, and giant radar towers monitoring all maritime movements in the strait, accidents occasionally happen.

The Bosphorus in Legend

The Bosphorus's English name comes from a Greek legend: Zeus had an affair with a beautiful women named Io. When Hera, his wife, discovered his infidelity, she turned Io into a cow and created a horsefly to sting her on the rump. Io jumped clear across the strait. Thus bous = cow, and poros = crossing-place: Bosphorus = "crossing-place of the cow."

Recent marine archeological research in the chill, deep waters of the Black Sea has revealed sunken cities on the underwater slopes along the Turkish coast.

Geological evidence supports the theory that in ancient times the northern end of the Bosphorus was blocked by earth and rock. The Black Sea had no outlet (like Lake Van today), and its water level was below that of the Aegean Sea, the Sea of Marmara, and the Bosphorus.

However, an earthquake destroyed the Bosphorus blockage, releasing a deluge of water from the Bosphorus into the Black Sea, raising the water level and flooding its coastal communities. So it may well be that the Bosphorus is the source of Noah's flood and the legend of Noah's Ark! (Mount Ararat is also in Turkey.)

The Bosphorus in History

The Bosphorus has been a waterway of the highest importance since ancient times. Ulysses passed through. Byzas, who founded Byzantium (later Constantinople, later Istanbul) sailed up and down looking for the perfect place to found his village.

In 1452, Mehmet the Conqueror ordered the construction of the mighty fortresses of Rumeli Hisarı(Fortress of Europe) and Anadolu Hisarı (Fortress of Anatolia) so he could control the strait and prevent reinforcements from reaching the besieged Byzantinecapital of Constantinople.


Rumeli Hisari Fortress

A speedboat zooms south past Rumeli Hisarıfortress and Fatih (Conqueror) Bridge.

To the Ottomans it was mostly an obstacle: each spring they had to ship their gigantic armies across the strait from Istanbul for campaigns in Anatolia, Syria and Persia.

During World War I, the Bosphorus was the key to the Black Sea and Russia. The Sultan held the key. The Entente powers wanted it. What they failed to get in battle they got by treaty, and British gunboats anchored outside Dolmabahçe Palace.

—by Tom Brosnahan

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