The Bosporus or Bosphorus Strait is a natural strait and an internationally significant waterway located in Turkey which is straddled by the city of Istanbul. The Bosporus connects the Black Sea to the Sea of Marmara and forms one of the continental boundaries between Asia and Europe. It also divides Turkey by separating Asia Minor from Thrace. It is the world's narrowest strait used for international navigation.
Most of the shores of the Bosporus Strait, except for the area to the north, are heavily settled, with the city of Istanbul's metropolitan population of 17 million inhabitants extending inland from both banks.
The Bosporus Strait and the Dardanelles Strait at the opposite end of the Sea of Marmara are together known as the Turkish Straits.
Sections of the shore of the Bosporus in Istanbul have been reinforced with concrete or rubble and those sections of the strait prone to deposition are periodically dredged.
Name The name of the strait comes from the Ancient Greek (), which was folk-etymologised as , i.e. "cattle strait" (like "Ox-ford"), from the genitive of 'ox, cattle' + 'passage', thus meaning 'cattle-passage', or 'cow passage'. This is a reference to the Greek mythological story of Io, who was transformed into a cow and condemned to wander the Earth until she crossed the Bosporus, where she met the Titan Prometheus, who comforted her by telling her that she would be restored to human form by Zeus and become the ancestor of the greatest of all heroes, Heracles (Hercules).
Io supposedly went ashore near Chrysopolis (present-day Üsküdar), which was named '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, which included a colossal statue of a cow (the name translating to 'heifer').
The English spelling with -ph- (Bosphor) is not justified by the ancient Greek name, and dictionaries prefer the spelling with -p-. However, -ph- occurs as a variant in medieval Latin (as Bosphor, and occasionally Bosphorus or Bospherus), and in medieval Greek sometimes as , giving rise to the French , the Spanish , the Italian and the Russian . The 12th-century Greek scholar John Tzetzes calls it (after Damalis), but he also reports that in popular usage the strait was known as during his day, the name of the most ancient northern harbour of Constantinople. In English, the preferred spelling tends to be Bosphorus.
Historically, the Bosporus was also known as the "Strait of Constantinople", or the Thracian Bosporus to distinguish it from the Cimmerian Bosporus in Crimea. These are expressed in Herodotus's Histories, 4.83; as , , and (), respectively. Other names used by Herodotus to refer to the strait include Chalcedonian Bosporus (, [], Herodotus 4.87), or Mysian Bosporus ().
The term eventually came to be used as the common noun , meaning "a strait", and was also formerly applied to the Hellespont in Classical Greek by Aeschylus and Sophocles.
Boğaziçi
Boğaziçi consists of those parts of Istanbul and overlapping administrative districts with a view of the Bosphorus. It is considered more particularly to consist of those parts of Istanbul that are situated north of the Golden Horn (Haliç), starting with the district of Beşiktaş on the European side of the Bosphorus. Thus it includes, from south to north, along the European shore, Beşiktaş, Ortaköy, Arnavutköy, Bebek, Rumelihisarı, Baltalimanı, Emirgan, İstinye, Yeniköy, Tarabya, Kireçburnu, Büyükdere and Sarıyer; and, along the Asian shore, Üsküdar, Beylerbeyi, Çengelköy, Vaniköy, Kandilli, Anadolu Hisarı, Kanlıca and Beykoz.
Geography As a maritime waterway, the Bosporus connects the Black Sea to the Sea of Marmara and thence to the Aegean and Mediterranean seas via the Dardanelles. It also connects various seas along the Eastern Mediterranean, the Balkans, the Near East, and Western Eurasia. Thus, the Bosporus allows maritime connections from the Black Sea all the way to the Mediterranean Sea and the Atlantic Ocean via Gibraltar, and to the Indian Ocean through the Suez Canal, making it a crucial international waterway, in particular for the passage of goods coming from Russia.
There is one very small island in the Bosporus just off Kuruçeşme. Now generally known as Galatasaray Island (Galatasaray Adası), this was given to the Armenian architect Sarkis Balyan by Sultan Abdülhamid II in 1880. The house he built on it was later demolished. The island became a walled garden and then a water sports centre, before it was given to the Galatasaray Sports Club, hence its name. However, in the 2010s it was completely overbuilt with nightclubs and the government had these torn down in 2017. It reopened exclusively to the Galatasaray club members in the summer of 2022.
Formation
The exact cause and date of the formation of the Bosporus remain a subject of debate among geologists. One recent hypothesis, dubbed the Black Sea deluge hypothesis, which was launched by a study of the same name in 1997 by two scientists from Columbia University, postulates that the Bosporus was flooded around 5600 BC (revised to 6800 BC in 2003) when the rising waters of the Mediterranean Sea and the Sea of Marmara broke through to the Black Sea, which at the time, according to the hypothesis, was a low-lying body of fresh water.
Many geologists, however, claim that the strait is much older, even if relatively young on a geologic timescale.
Present morphology The limits of the Bosporus are defined as the line connecting the lighthouses of Rumeli Feneri and Anadolu Feneri in the north, and between the Ahırkapı Feneri and the Kadıköy İnciburnu Feneri in the south ("Fener" is Turkish for lighthouse). Between these limits, the strait is long, with a width of at the northern entrance and at the southern entrance. Its maximum width is between Umuryeri and Büyükdere Limanı, and minimum width is between Kandilli Point and Aşiyan.
The depth of the Bosporus varies from in midstream with an average of . The deepest point is between Kandilli and Bebek, at . The shallowest locations are off Kadıköy İnciburnu at and off Aşiyan Point at .
The southbound flow of water is 16 000 m3/s (fresh water at the surface) and the northbound flow is 11 000 m3/s (salt water near the bottom). Dan Parsons and researchers at the University of Leeds School of Earth and Environment describe a Black Sea undersea river.
The Golden Horn is an estuary off the main strait that historically acted as a moat to protect Constantinople from attack, as well as providing sheltered anchorage for the imperial navies of various empires until the 19th century, after which it became a historic neighbourhood at the heart of Istanbul.
Newer explorations Before the 20th century it was already known that the Black Sea and the Sea of Marmara flow into each other in a geographic example of "density flow". Then in August 2010, a continuous 'underwater channel' of suspension composition was discovered flowing along the floor of the Bosporus, which would be the sixth largest river on Earth if it were on land. The 2010 team of scientists, led by the University of Leeds, used a robotic "yellow submarine" to observe detailed flows within this "undersea river", scientifically referred to as a submarine channel, 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.
The team studied the detailed flow within these channels and its findings included that:
The central tenet of the Black Sea deluge hypothesis is that as the ocean rose at the end of the last Ice Age when the massive ice sheets melted, the sealed Bosporus was overwhelmed by a spectacular flood that increased the then fresh water Black Sea Lake by 50%, and drove people back from the shores for many months. This hypothesis was supported by the findings of 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. Driven out by the rapidly rising water, which must have been terrifying and inexplicable, people spread to all corners of the Western world carrying the story of a major flood. 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.
The first images of these submarine channels showing them to be of great size, were obtained in 1999 during a NATO SACLANT Undersea Research project using jointly the NATO RV Alliance, and the Turkish Navy survey ship Çubuklu. In 2002, a survey carried out on board the Ifremer RV Le Suroit for BlaSON project (Lericolais, et al., 2003) completed the multibeam mapping of this underwater channel fan-delta. A complete map was published in 2009 using these previous results together with high quality mapping obtained in 2006 (by researchers at Memorial University of Newfoundland who were project partners in the study).
The project was led by Jeff Peakall and Daniel Parsons at the University of Leeds, in collaboration with the University of Southampton, Memorial University of Newfoundland, and the Institute of Marine Sciences. The survey was run and coordinated from the Institute of Marine Sciences research ship, the R/V Koca Piri Reis.
Villages The shores of the Bosporus were once lined with small fishing villages that had grown up since Byzantine times but really came into their own in the 19th century. Until the early 20th century most were only accessible by boat (known as caiques) along the Bosporus since there were no coast roads. Today the villages are no more than suburbs of Greater Istanbul but many retain the memory of their original village status in the suffix -köy ('village') to their names. e.g. Ortaköy, Yeniköy, Arnavutköy, Çengelköy and Vaniköy. These villages often had distinct identities associated with agriculture: Arnavutköy, for example, was associated with strawberry-growing while Çengelköy was famous for its sweet cucumbers.
Human history As part of the only passage between the Black Sea and the Mediterranean, the Bosporus has always been of great importance from a commercial and military point of view, and it remains strategically important today. It is a major sea access route for numerous countries, including Russia and Ukraine. Control over it has been an objective of a number of conflicts in modern history, notably the Russo-Turkish War (1877–78), 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. In 2022 during the Russian invasion of Ukraine the Bosporus' importance as a route by which grain reached the world was thrown into sharp profile.
Ancient Greek, Persian, Roman and Byzantine eras (pre-1453)
The strategic importance of the Bosporus dates back millennia. In the 5th century BC the Greek city-state of Athens, which depended on grain imports from the Black Sea ports of Scythia, maintained critical alliances with cities which controlled the straits, such as the Megarian colony of Byzantium.
In an attempt to subdue the Scythian horsemen who roamed across the north of the Black Sea, the Persian King Darius I the Great () crossed the Bosporus, then marched towards the River Danube. His army crossed the Bosporus using an enormous bridge made by connecting boats. This bridge essentially connected the farthest geographic tip of Asia to Europe, encompassing at least some 1,000 metres of open water. Years later, Xerxes I would construct a similar boat bridge across the Dardanelles (Hellespont) strait (480 BC), during his invasion of Greece.