Bosporus is located in Europe
Coordinates41°07′10″N 29°04′31″E / 41°07′10″N 29°04′31″E / 41.11944; 29.07528Turkey
Max. length31 km (19 mi)
Min. width700 m (2,300 ft)
Max. depth110 m (360 ft)
Bosporus is located in Europe
A map depicting the locations of the Turkish Straits, with the Bosporus in red, and the Dardanelles in yellow. The territory of Turkey is highlighted in green.
Location of the Bosporus (red) relative to the Dardanelles (yellow) and the Sea of Marmara.
Close-up satellite image of the Bosporus strait, taken from the ISS in April 2004. The body of water at the top is the Black Sea, the one at the bottom is the Marmara Sea, and the Bosporus is the winding waterway that connects the two. The western banks of the Bosporus constitute the geographic starting point of the European continent, while the banks to the east are the geographic beginnings of the continent of Asia. The city of Istanbul is visible along both banks.
Aerial view of the Bosporus taken from its northern end near the Black Sea (bottom), looking south (top) toward the Marmara, with the city center of Istanbul visible along the strait's hilly banks.

The Bosporus (s/) or Bosphorus (ər-/;[1] Ancient Greek: Βόσπορος Bosporos [bós.po.ros]; also known as the Strait of Istanbul; Turkish: İstanbul Boğazı) is a narrow, natural strait and an internationally significant waterway located in northwestern Turkey. It forms part of the continental boundary between Europe and Asia, and divides Turkey by separating Anatolia from Thrace. It is the world's narrowest strait used for international navigation, the Bosporus connects the Black Sea with the Sea of Marmara, and, by extension via the Dardanelles, the Aegean and Mediterranean seas.

Most of the shores of the strait are heavily settled, straddled by the city of Istanbul's metropolitan population of 17 million inhabitants extending inland from both coasts.

Together with the Dardanelles, the Bosporus forms the Turkish Straits.


The name of the channel comes from the Ancient Greek Βόσπορος (Bosporos), which was folk-etymologised as βοὸς πόρος, i.e. "cattle strait" (or "Ox-ford"[2]), from the genitive of bous βοῦς "ox, cattle" + poros πόρος "passage", thus meaning "cattle-passage", or "cow passage".[3] This is in reference to the mythological story of Io, who was transformed into a cow, and was subsequently condemned to wander the Earth until she crossed the Bosporus, where she met the Titan Prometheus, who comforted her with the information that she would be restored to human form by Zeus and become the ancestress of the greatest of all heroes, Heracles (Hercules).

The site where Io supposedly went ashore was near Chrysopolis (present-day Üsküdar), and was named 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, which included a colossal statue of a cow (the name Damalis translating to "calf").[4]

The English spelling with -ph-, Bosfor has no justification in the ancient Greek name, and dictionaries prefer the spelling with -p-[1] but -ph- occurs as a variant in medieval Latin (as Bosfor, and occasionally Bosforus, Bosferus), and in medieval Greek sometimes as Βόσφορος,[5] 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,[6] the name of the most ancient northern harbour of Constantinople.

Historically, the Bosporus was also known as the "Strait of Constantinople", or the Thracian Bosporus, in order to distinguish it from the Cimmerian Bosporus in Crimea. These are expressed in Herodotus' Histories, 4.83; as Bosporus Thracius, Bosporus Thraciae , and Βόσπορος Θρᾴκιος, respectively. Other names by which the strait is referenced by Herodotus include Chalcedonian Bosporus (Bosporus Chalcedoniae, Bosporos tes Khalkedonies, Herodotus 4.87), or Mysian Bosporus (Bosporus Mysius).[7]

The term eventually came to be used as common noun βόσπορος, meaning "a strait", and was also formerly applied to the Hellespont in Classical Greek by Aeschylus and Sophocles.