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This article is about the strait in Turkey. For the strait in Russia, see Eastern Bosphorus. For the surrounding neighbourhoods of Istanbul, see Boğaziçi. For the university in Turkey, see Boğaziçi University. For the ancient Hellenic state, see Bosporan Kingdom.
Satellite image of the Bosphorus, taken from the International Space Station in April 2004.
Aerial view of the Bosphorus from north (bottom) to south (top), with the city center of Istanbul at the southern end.

The Bosphorus (/ˈbɒsfərəs/), also Bosporus (/ˈbɒspərəs/), from Greek Βόσπορος (Vosporos); Turkish: Boğaziçi) is a strait that forms part of the boundary between Europe and Asia. The Bosporus, the Sea of Marmara, and the Dardanelles strait to the southwest together form the Turkish Straits. The world's narrowest strait used for international navigation, the Bosporus connects the Black Sea with the Sea of Marmara (which is connected by the Dardanelles to the Aegean Sea, and thereby to the Mediterranean Sea).

The limits of the Bosporus are defined as the connecting line between the lighthouses Rumeli Feneri and Anadolu Feneri in the north and between the Ahırkapı Feneri and the Kadıköy İnciburnu Feneri in the south. Between the limits, the strait is 31 km (17 nmi) long, with a width of 3,329 m (1.798 nmi) at the northern entrance and 2,826 m (1.526 nmi) at the southern entrance. Its maximum width is 3,420 m (1.85 nmi) between Umuryeri and Büyükdere Limanı, and minimum width 700 m (0.38 nmi) between Kandilli Point and Aşiyan. This part of the strait is a dangerous point for maritime traffic: a 45-degree course alteration is required, and the current can reach 7 to 8 knots (3.6 to 4.1 m/s). To the south, at Yeniköy, the necessary course alteration is 80 degrees. All the dangers and obstacles characteristic of narrow waterways are present and acute in this critical sea lane. At the above mentioned turns (Kandilli and Yeniköy) where significant course alterations have to be made, the rear and forward sights are totally blocked prior to and during the course alteration. Ships approaching from the opposite direction cannot be seen around these bends. The risks posed by geography are multiplied by the heavy ferry traffic across the strait, linking the European and Asian sides of the city.

The depth of the Bosporus varies from 13 to 110 m (43 to 361 ft) in midstream with an average of 65 m (213 ft). The deepest location is between Kandilli and Bebek with 110 m (360 ft). The most shallow locations are off Kadıköy İnciburnu on the northward route with 18 m (59 ft) and off Aşiyan Point on the southward route with 13 m (43 ft).[1] The Golden Horn is an estuary off the main straits that acted as a moat to protect Old Istanbul from attack, as well as providing a sheltered anchorage for the imperial navy until the 19th century.

Most of the shores of the strait are heavily populated, straddled as it is by the city of Istanbul (with a metropolitan area population in excess of 12 million inhabitants) which extends inland from both coasts.

It has been known since before the 20th century that the Black Sea and the Sea of Marmara flow into each other in an example of a density flow and in August 2010 a continuous 'underwater channel' of suspension composition was discovered to flow along the floor of the Bosporus which would be the sixth largest river on Earth if it were to be on land. The study of the water and wind erosion of the straits relates to that of its formation. Sections of the shore have been reinforced with concrete or rubble and sections of the strait prone to deposition are periodically dredged.


The Bosporus is also known as "Strait of Constantinople", or as "Istanbul Strait" (Turkish: İstanbul Boğazı). To distinguish it from the Cimmerian Bosporus, it was anciently known as the Thracian Bosporus (Herodotus 4.83; Bosporus Thracius, Bosporus Thraciae , Βόσπορος Θρᾴκιος, also Chalcedonian Bosporus, Bosporus Chalcedoniae, Bosporos tes Khalkedonies, Herodotus 4.87, or Mysian Bosporus, Bosporus Mysius).[2] The term could also be used as common noun βόσπορος, meaning "a strait", and was also applied to the Hellespont in Classical Greek (Aeschylus, Sophocles).

The Greek name Βόσπορος (Bosporos) was folk-etymologized as from βοὸς πόρος, i.e. "cattle strait" (or "Ox-ford"[3]), from the genitive of bous βοῦς "ox, cattle" + poros πόρος "passage", thus "cattle-passage", or "cow passage"[4] in reference to Io from Greek mythology who was transformed into a cow and condemned to wander the earth until she crossed the Bosporus where she met Prometheus. This folk etymology was canonized by Aeschylus in Prometheus Bound (v. 734f.), where Prometheus prophesies to Io that the strait would be named after her. The site where Io supposedly went ashore was near Chrysopolis, was named he Bous "the Cow". The same site was also known as Damalis, as it was where the Athenian general Chares had erected a monument to his wife Damalis. This monument included a colossal statue of a cow (the name Damalis translating to "calf").[5] The actual etymology of the name is more likely from the verb βύζω or βύω, "to fill up, clog up, plug, stop", referring to a "plugged" or stopped-up passage, perhaps also cognate with the name of Byzantium (Hesychius has βύζαντες: πλήθοντες, i.e. buzantes meaning "filled up").[citation needed]

The spelling with -ph-, as Bosphorus, has no justification in the ancient Greek name, but it occurs as a variant in medieval Latin (as Bosphorus, and occasionally Bosforus, Bosferus), and in medieval Greek sometimes as Βόσφορος,[6] giving rise to the French form Bosphore, Spanish Bósforo, and Russian Босфор. The 12th-century Greek scholar John Tzetzes calls it Damaliten Bosporon (after Damalis), but he also reports that in popular usage the strait was known as Prosphorion during his day,[7] the name of the main northern harbour of Constantinople.


A map depicting the location of the Bosphorus (red) relative to the Dardanelles (yellow) and the Sea of Marmara, which together form the Turkish Straits.

The exact cause for the formation of the Bosporus remains the subject of debate among geologists. Thousands of years ago, the Black Sea became disconnected from the Aegean Sea. The Black Sea deluge theory (reinforced in credibility by a study of the same name of 1997 by two scientists from Columbia University) contends that the Bosporus was formed about 5600 BC when the rising waters of the Mediterranean/Sea of Marmara breached through to the Black Sea, which at the time (according to the theory) was a low-lying body of fresh water.

It is also said in myth that floating rocks known as the Symplegades or Clashing Rocks once crushed any ship that attempted passage of the Bosporus until the hero Jason obtained passage, whereupon the rocks became fixed, and Greek access to the Black Sea was opened.

Ancient Greece, Persia, Rome, the Byzantines and the Ottoman Empire[edit]


As part of the only passage between the Black Sea and the Mediterranean, the Bosporus has always been of great commercial and strategic importance. The Greek city-state of Athens in the 5th century BC, which was dependent on grain imports from Scythia, maintained critical alliances with cities which controlled the straits, such as the Megarian colony Byzantium.

Persian King Darius I the Great, in an attempt to subdue the Scythian horsemen who roamed across the north of the Black Sea, crossed through the Bosporus, then marched towards the Danube River. His army crossed the Bosporus over an enormous bridge made by connecting Achaemenid boats.[8] This bridge essentially connected the farthest geographic tip of Asia to Europe, encompassing at least some 1000 meters of open water if not more.[9] Years later, a similar boat bridge would be constructed by Xerxes I on the Dardanelles (Hellespont) strait, during his invasion of Greece. Byzantines called the Bosporus "Stenon" and most important toponyms of it Bosporios Akra, Argyropolis, St. Mamas, St. Phokas, Hestiai or Michaelion, Phoneus, Anaplous or Sosthenion in European side and Hieron tower, Eirenaion, Anthemiou, Sophianai, Bithynian Chryspolis in Asian side in this era [10]

The strategic significance of the strait was one of the factors in the decision of the Roman Emperor Constantine the Great to found there in AD 330 his new capital, Constantinople, which came to be known as the capital of the Eastern Roman Empire. On 29 May 1453 it was conquered by the emerging Ottoman Empire. In fact, as the Ottoman Turks closed in on Constantinople, they constructed a fortification on each side of the strait, Anadoluhisarı (1393) and Rumelihisarı (1451).

Strategic importance[edit]


The Bosporus remains strategically important. It is a major sea access route for Russia and Ukraine. Control over it has been an objective of a number of hostilities in modern history, notably the Russo–Turkish War, 1877–1878, as well as of the attack of the Allied Powers on the Dardanelles during the 1915 Battle of Gallipoli in the course of World War I.

At its peak in the 16th through the 18th centuries, the Ottoman Empire had wrested control of the entire Black Sea area, which was for the time an "Ottoman lake", on which Russian warships were prohibited.[11]

Subsequently, several international treaties have governed vessels using the waters. Under the Treaty of Hünkar Iskelesi of 1833, the Bosporus and Dardanelles straits were to be closed on Russian demand to naval vessels of other powers.[12] Following World War I, the 1920 Treaty of Sèvres demilitarized the strait and made it an international territory under the control of the League of Nations. This was amended under the 1923 Treaty of Lausanne, which restored the straits to Turkish territory—but allowed all foreign warships and commercial shipping to traverse the straits freely. Turkey eventually rejected the terms of that treaty, and subsequently Turkey remilitarized the straits area. The reversion was formalized under the Montreux Convention Regarding the Regime of the Turkish Straits of July 1936. That convention, which is still in force, treats the straits as an international shipping lane save that Turkey retains the right to restrict the naval traffic of non-Black Sea states.



Fatih Sultan Mehmet Bridge (1988) and the Bosphorus strait


Fatih Sultan Mehmet Bridge (1988) as seen from the Rumelian Castle (1452)

The waters of the strait are traversed by numerous ferries. Two suspension bridges cross the Bosporus. The first of these, the Bosporus Bridge, is 1,074 m (3,524 ft) long and was completed in 1973. The second, named Fatih Sultan Mehmet (Bosporus II) Bridge, is 1,090 m (3,576 ft) long, and was completed in 1988 about 5 km (3 mi) north of the first bridge. The Bosporus Bridge forms part of the O1 Motorway, while the Fatih Sultan Mehmet Bridge forms part of the Trans-European Motorway.

Construction of a third suspension bridge, the Yavuz Sultan Selim Bridge, began on May 29, 2013; opening is planned for May 29, 2015.[17] The bridge will be built near the northern end of the Bosporus, between the villages of Garipçe on the European side and Poyrazköy on the Asian side.[18] It will be part of the "Northern Marmara Motorway", which will be further integrated with the existing Black Sea Coastal Highway, and will allow transit traffic to bypass city traffic,

The Marmaray project, featuring a 13.7 km (8.5 mi) long undersea railway tunnel, opened on 29 October 2013.[19] Approximately 1,400 m (4,593 ft) of the tunnel runs under the strait, at a depth of about 55 m (180 ft).

An undersea water supply tunnel with a length of 5,551 m (18,212 ft),[20] named the Bosporus Water Tunnel, was constructed in 2012 to transfer water from the Melen Creek in Düzce Province (to the east of the Bosporus strait, in northwestern Anatolia) to the European side of Istanbul, a distance of 185 km (115 mi).[20][21]

The Eurasia Tunnel is a road tunnel between Kazlicesme and Goztepe, which began construction in February 2011 and is expected to open in 2014.

The phrase "swim the Bosporus" or "crossing the Bosporus" is used to indicate religious conversion to the Eastern Orthodox Church.

Submarine channel[edit]


In 2010, a team of scientists led by the University of Leeds used a robotic "yellow submarine" to observe detailed flows within an "undersea river" for the first time. Submarine channels are similar to land rivers, but they are formed by density currents—underwater flow mixtures of sand, mud and water that are denser than sea water and so sink and flow along the bottom. These channels are the main transport pathway for sediments to the deep sea where they form sedimentary deposits. These deposits ultimately hold not only untapped reserves of gas and oil, they also house important secrets—from clues on past climate change to the ways in which mountains were formed.[22]




The central tenet of the Black Sea Deluge theory is that as the ocean rose 238 ft at the end of the last Ice Age when the massive ice sheets melted, the sealed Bosporus was overtopped in a spectacular flood that increased the then fresh water Black Sea Lake 50%, and drove people from the shores for many months. This was proven by undersea explorer Robert Ballard, who discovered settlements along the old shoreline; scientists dated the Flood to 7500 BP or 5500 BC from fresh-salt water microflora. The peoples driven out by the constantly rising water, which must have been terrifying and inexplicable, spread to all corners of the Western world carrying the story of the Great Flood, how it probably entered most religions. As the waters surged, they scoured a network of sea-floor channels less resistant to denser suspended solids in liquid, which remains a very active layer today.

It is one of the possibilities for the biblical event of Noah's flood. The first images of these submarine channels were obtained in 1999, showing them to be of great size[24] in the frame of a NATO SACLANT Undersea Research project using jointly the NATO RV Alliance, and the Turkish Navy survey ship Çubuklu. In 2002, a survey was carried out on board the Ifremer RV Le Suroit for BlaSON project (Lericolais, et al., 2003[25]) completed the multibeam mapping of this underwater channel fan-delta. A complete map was published in 2009 [26] using these previous results with high quality mapping obtained in 2006 (by researchers at Memorial University, Newfoundland, Canada who are project partners in this study.)



The researchers estimate that the river—known as a submarine channel—would be the sixth largest river in the world if it were on land based on the amount of water flowing through it.[22]

Panoramic view of a portion of the Bosphorus, as seen from the Ulus neighbourhood on the European side, with the Fatih Sultan Mehmet Bridge (1988) at left and the Bosphorus Bridge (1973) at right.


Ottoman era waterfront houses (yalı) on the Bosphorus.


Ottoman era waterfront houses (yalı) on the Bosphorus.
Ottoman era waterfront houses (yalı) on the Bosphorus.





Image gallery[edit]

See also[edit]


  1. ^ a b "Türk Boğazları ve Marmara Denizi'nin Coğrafi Konumu-İstanbul Boğazı" (in Turkish). Denizcilik. Retrieved 2010-09-18. [dead link]
  8. ^ Polybios, Historiae IV, 39, 16; Özhan Öztürk. Pontus: Antik Çağ’dan Günümüze Karadeniz’in Etnik ve Siyasi Tarihi Genesis Yayınları. Ankara, 2011 pp. 28–29
  9. ^ Herodotus (Translation by George Rawlinson, Sir Henry Creswicke Rawlinson, Sir John Gardner Wilkinson) (1859). The History of Herodotus: a new English version, Volume 3. John Murray. pp. 77 (Chp. 86). 
  10. ^ Özhan Öztürk. Pontus: Antik Çağ’dan Günümüze Karadeniz’in Etnik ve Siyasi Tarihi Genesis Yayınları. Ankara, 2011 pp. 28–32
  11. ^ "Turkey - Köprülü Era". 2007-03-24. Retrieved 2010-06-08. 
  12. ^ "Turkey - External Threats and Internal Transformations". 2007-03-24. Retrieved 2010-06-08. 
  13. ^ "Foreign Policy Research Institute: The Turkish Factor in the Geopolitics of the Post-Soviet Space (Igor Torbakov)". 2003-01-10. Retrieved 2010-06-08. 
  15. ^ "Russia's relations with Turkey". Retrieved 2010-06-08. 
  16. ^ "Today's Zaman: Against who and where are we going to stand? (Ali Bulaç)". Retrieved 2010-06-08. 
  17. ^ Yavuz Sultan Selim Köprüsü "3. köprünün ismi Yavuz Sultan Selim". NTV-MSNBC (in Turkish). 2013-05-29. Retrieved 2013-05-29. 
  20. ^ a b CNN Türk: "Melen hattı Boğaz'ı geçti" (21-05-2012)
  21. ^ Nayır, Mehmet (2012-05-19). "Melen Boğaz’ı geçiyor". Sabah Ekonomi (in Turkish). Retrieved 2012-06-11. 
  22. ^ a b
  23. ^ "Robotic sub. records flow of undersea river" (August 2, 2010.)

External links[edit]
