The Bosphorus, İstanbul Boğazı in Turkish, is the winding sea channel of about 30 km that joins the Black Sea to the Sea of Marmara and splits İstanbul into its European and Asian halves. For the countries around the Black Sea it is the only way out to the Mediterranean, and the settled shores on both sides are called Boğaziçi. The old name, Bosporos, joins the Greek words for ox and passage, and myth ties it to Io, whom Zeus turned into a heifer and who swam across the strait here.
Its two shores come closest between Rumelihisarı and Anadoluhisarı, less than a kilometre apart, where the two fortresses, Rumeli Hisarı and Anadolu Hisarı, still face each other; the deepest water lies between Bebek and Kandilli. The channel makes twelve sharp bends, and its currents are famous. Water from the Black Sea, less salty, runs south on the surface, strongest in the middle reaches from Kandilli southwards, while the heavier, saltier water of the Marmara flows north along the bottom. When strong southerly winds pile Marmara water into the mouth, a reverse surface current called the orkoz can form, sometimes strong enough to stop the city ferries. Because it links seas of different salinity and temperature, the strait is also a migration route for fish: bonito (palamut), bluefish (lüfer), horse mackerel (istavrit) and tuna (orkinos) are the kinds most often seen in İstanbul.
In the eighteenth century the sultan and his court turned from the historic peninsula to these shores, and the best known of the palaces that survive on them are Dolmabahçe, Çırağan and Beylerbeyi, along with pavilions such as Küçüksu, Beykoz and Adile Sultan. Between them run the yalıs, the timber waterside mansions of the Ottoman elite: long, mostly two-storey houses whose upper floors jut out over the sea on brackets, open to the water at the front and closed off by high walls towards the lane behind, with boathouses, sea baths and fish houses to complete them. Each shore had its own residents — sultans and statesmen at Beşiktaş, Ortaköy and Kuruçeşme, officials of the Bâbıâli at Bebek, non-Muslim families at Arnavutköy, the summer houses of embassies and foreigners at Yeniköy, Tarabya and Büyükdere. After the First World War many owners could no longer keep them up, and a good number changed hands or were lost to fire.
Three suspension bridges now cross the strait: the 15 Temmuz Şehitler Köprüsü, formerly the Boğaziçi Köprüsü, completed in 1973 between Ortaköy and Beylerbeyi; the Fatih Sultan Mehmet Köprüsü of 1988, between Rumeli Hisarüstü and Kavacık; and the Yavuz Sultan Selim Köprüsü, between Garipçe in Sarıyer and Poyrazköy in Beykoz. The Marmaray rail tunnel runs beneath the water, linking the two sides of the city by train.
Getting there
The easiest way to see the strait is from the water. Eminönü is the starting point both for the ferries on the Bosphorus lines and for the tourist boats that make Bosphorus trips, and city ferries, passenger boats, sea taxis and car ferries also cross between the two shores.
When to go
- Climate
- Across İstanbul as a whole, monthly mean temperatures run from 6.8 °C in January to 24.7 °C in August; the mean stays between 15 and 25 °C in May, June, July, August, September and October; rainfall is heaviest in December (99 mm) and lightest in July (22 mm). Long-term means for 1950-2025 from the Turkish State Meteorological Service (MGM).
