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The Bosphorus, in the lower part of the picture İstanbul, which lies in both Europe (left) and Asia (right).  Lower left the Golden Horn.
The Bosphorus, in the lower part of the picture İstanbul, which lies in both Europe (left) and Asia (right). Lower left the Golden Horn .
Connects waters Sea of ​​Marmara
with water Black Sea
Separates land mass Asia
of land mass Europe
Geographical location 41 ° 7 '  N , 29 ° 5'  E Coordinates: 41 ° 7 '  N , 29 ° 5'  E
Bosporus (Turkey)
length 30 km
Smallest width 700 m
Coastal towns Istanbul
bridges Bridge of the Martyrs of July 15th , Fatih Sultan Mehmet Bridge , Yavuz Sultan Selim Bridge
tunnel Marmaray , Eurasia Tunnel

The Bosphorus ( ancient Greek Βόσπορος , cattle ford ' , from ancient Greek βοῦς boũs , cattle, ox' and ancient Greek πόρος póros , path, ford '; Turkish Boğaz, gullet', or Karadeniz Boğazı for 'throat of the Black Sea'; outdated, street from Constantinople ') is a strait between Europe and Asia , which connects the Black Sea (in ancient times: Pontos Euxeinos) with the Marmara Sea (in ancient times: Propontis); therefore it represents a section of the southern inner Eurasian border . On both sides is the city ​​of Istanbul , whose geography it significantly shapes. The Bosporus is around 30 kilometers long and 700 to 2500 meters wide. In the middle, the depth varies between 36 and 124 meters (near Bebek ). Within the Bosphorus on the western side lies the Golden Horn , an elongated bay and a natural harbor that has been in use for a long time.

The rights of passage for international shipping were regulated in the 1936 Treaty of Montreux .


The origin of the Bosporus has not yet been clarified with certainty. 1,997 attended the American marine biologist William Ryan and Walter C. Pitman with its flood - hypothesis stir. It says that the Bosphorus is only about 7500 years old. Before that, the Black Sea was an inland body of water about 120 meters below sea level today. In the course of the Holocene sea transgression due to the melting of Ice Age glaciers, it was around the sixth millennium BC. BC the Mediterranean broke into the Black Sea via the Sea of ​​Marmara and the Bosporus. The very flat bottom of the relatively wide waterway cut deep into the rock is interpreted as an indication of the very high flow speed of the water when it was formed.

Both the timing and the course of this event are highly controversial. Environmental researchers from the USA and Canada (Teofilo Abrajano, Rensselaer Polytechnic Institute , Ali Aksu, University of Newfoundland) carried out analyzes of the sediments in the Sea of ​​Marmara, which they believe refute the Flood hypothesis. According to this, the water has been flowing continuously from the Black Sea into the Mediterranean since the end of the last Ice Age .

Water flow

A general cargo ship passes the Bosphorus in Istanbul

A strong upper current flows from the Black Sea, and at a depth of about 40 meters a weaker undercurrent flows in the opposite direction, driven by the higher density of the Mediterranean water . The salt content in the Mediterranean is about twice as high as in the Black Sea. The Mediterranean is an arid (dry) sea - evaporation exceeds the water inflow from the feeding rivers. In contrast, the water inflow into the Black Sea from its feeding rivers is greater than the evaporation. Because of the water-rich tributaries into the Black Sea (especially the Danube , but also the Dnepr , Dniester , Don , Southern Bug , among others ), the excess water of the Black Sea is around 300 km³ per year. The water from the Black Sea flows over the Bosphorus, the Marmara Sea and the Dardanelles into the Aegean and the Mediterranean Sea at an average speed of 3  knots (up to 8 knots in places).

In early antiquity , the Greeks could not sail their ships through the Bosphorus from late spring to summer. During this time, northeast winds blew and the current speed increased to an average of 4 knots against which the Greek ships could not cross. Her rudder speed was also insufficient to counter the current. Only with the advent of stronger rowing boats ( Pentekonteren ) could the Greeks get their ships through the Bosporus into the Black Sea all year round.

Winds from north to northeast prevail on the Bosporus. The tides are very weak. In rare southerly winds, the surface water currents occasionally turn north.


Estuary into the Black Sea

The Bosporus (Turkish: İstanbul Boğazı) is one of the world's most important waterways . It enables important coastal strips of the countries bordering the Black Sea - including Russia , Turkey , Ukraine , Romania , Bulgaria and Georgia - maritime access to the Mediterranean Sea and thus access to international sea trade. In addition to agricultural goods and industrial products, oil also has a decisive share in the large volume of transport on this route. In particular, the countries bordering the eastern Black Sea and their hinterland connected by pipelines are regarded as oil suppliers of the 21st century, but at the same time politically as regions of unrest. After a Greenpeace campaign that drew attention to the risk of accidents for shipping traffic, the requirements for oil tankers to pass through were tightened at the end of 2002 . Around 50,000 ships pass through this strait each year. In the year the Treaty of Montreux was signed (1936) there were only 4,500.

In April 2012, the Turkish Prime Minister Erdoğan expressed his government's plans to relieve the Bosphorus through the Istanbul Canal, which was being built at the same time .


The Bosporus was already mentioned in ancient legends. On his journey to Colchis, Jason had to pass the life-threatening Symplegaden - two mythological rock islands that lie at the confluence of the Bosporus into the Black Sea.

The name Bosporus (cow or ox ford) comes from the fact that, according to legend, Io, who was transformed into a cow, swam over here on her flight.

When the term Bosporus was also used for other straits in ancient times , the Strait of Constantinople was called the Thracian Bosporus - to distinguish it from the Cimeric Bosporus or the Cimmerian Bosporus ( Strait of Kerch ).

Bosporus map around 1888

The Persian King Dareios I had in the 6th century BC BC build the ship bridge over the Bosporus , which is how his supposedly 700,000 strong army crossed for his campaign against the Scythians .

The great powers that controlled the Bosporus in the course of history (Eastern Roman Empire, Ottoman Empire) also sought control over the Black Sea. Sultan Bayezid I had the Gelibolu Shipyard built in 1390 to control the Bosporus and thus the shipping route between Constantinople (now Istanbul) and the Black Sea. Constantinople itself was not yet Ottoman at the time.

For this purpose, he also introduced ship inspections for all ships that wanted to pass through the Bosporus, and possibly also refused passage. The Anadolu Hisarı fortress (on the Asian side) was also built to control the Bosphorus . Later, in preparation for the siege and conquest of Constantinople , Mehmed II had the fortress Rumeli Hisarı (on the European side) built - exactly opposite the fortress Anadolu Hisarı. This gave the Ottoman Empire full control over access to the Black Sea. For a certain time, ships flying the flag of the Republic of Venice or the Republic of Genoa were granted free and unhindered passage to their colonies in the Black Sea; later they had to acquire a travel permit (izn-i sefine) and pay a tax. After 1484 (after the conquest of Kili and Akkirman under Bayezid II ), all ships flying a foreign flag were denied passage through the Bosporus. Due to the complete isolation of the Black Sea region from international trade, this region became the internal sea of ​​the Ottoman Empire in the 16th century. Initially, the entire Black Sea coast was under Ottoman rule. A privileged fleet of 120 ships (Unkapani kapan-i dakik; 175 tons of cargo each) transported grain from the Danube Delta and the Anatolian Black Sea coast on behalf of the empire. In addition, merchant ships were on their own account and had to submit an application for each voyage.

Later Russia conquered parts of the northern Black Sea coast (1739 Azov fortress , 1769 Taygan, 1778 founding of the port cities of Kerson and 1794 Odessa, 1783 Russian conquest of Crimea), and there was free trade with these areas, which was particularly popular with the Greeks from the Aegean (then under Ottoman rule). The captains of the departing ships had to guarantee that the entire crew would return, as there was a great need for qualified (Greek) seafarers in the Russian fleet and it had already largely been recruited from Greek seamen from the Ottoman domain. In later years, the captain even had to present a guarantee document (monetary guarantee) from his home community or a wealthy guarantor in Istanbul. The cases of (allegedly) deceased en route - and therefore no longer returning - seafarers were strictly investigated.

This status was maintained until 1774 when the Treaty of Küçük Kaynarca was signed. By the beginning of the 18th century, the Ottoman Empire had denied entry to the Black Sea for all ships flying a foreign flag, including merchant ships, including the smallest of boats. So the region remained under total Ottoman control. After 1774 Russian ships were allowed to cross the Bosporus and around 1800 also the ships of other European countries (1783 Austria, 1802 France and Great Britain). However, Russian ships were prohibited from transporting certain goods across the Bosporus. In particular, the Ottomans wanted to prevent grain from being transported further, as they themselves had a great need for it.

Russian warships, however, were strictly denied passage through the Bosporus, even when attempts were made to request passage for unarmed Russian warships. This should be transported as a separate load on merchant ships through the Bosporus.

The ban on the passage of Russian warships was first relaxed when Russia offered the Ottoman Empire military assistance on the occasion of Napoleon's Egyptian campaign (1798-1801). The Ottoman Empire allowed Russian warships to pass through for the duration of the war. When the 7th  Russo-Turkish War (1806–1812) broke out, the Ottomans signed an assistance pact with Great Britain (1809 in Kala-i Sultaniye) - in the event of a French attack. The British warships were granted the right to sail to the southern entrance of the Bosporus.

In the Treaty of Hünkâr İskelesi (1833) Russian ships were granted the right of passage, and the Ottoman government undertook to close the Bosporus to ships from all countries in the event of war. Because of the loud protests from Great Britain and France, this treaty did not last long. According to the London Treaty of 1841, the Bosphorus had to remain closed to all warships in peacetime - only smaller warships of allied nations were allowed to pass - after approval by a special commissioner. Thus the question of the passage through the Bosporus became a matter for the great powers.

In the following Crimean War (1853 to 1856) France and Great Britain sided with the Ottoman Empire and sent their navies to the Black Sea.

After the Crimean War ( Third Peace of Paris - 1856) the Bosphorus had the status of an international waterway, but remained closed to warships. The Ottoman Empire and Russia were prohibited from maintaining a navy in the Black Sea. However, with the London Treaty of 1871 Russia was allowed a navy of war in the Black Sea, and allied countries were allowed warships to cross the Bosporus during peacetime. This status was retained until the First World War.

In the Treaty of Edirne , which was signed after the Greek riots (1921), spurred on by Great Britain, France and Russia, merchant ships of all countries were granted free passage through the Bosporus.

In the Straits Agreement, which was signed in Montreux on July 20, 1936 , Turkey was granted sovereignty over the Bosporus, international rights of passage were regulated and Turkey's right to block the straits in the event of war. The signatory states were Turkey, Great Britain, France, Japan, USSR, Bulgaria, Romania, Greece and Yugoslavia. Italy did not join the agreement until 1938.

Historical defenses (according to Meyer's Lexicon 1888)

"The coastal works of the Bosphorus, which are supposed to defend it against an enemy coming from the Black Sea, consist of four groups.

The northernmost group extends to Vöjük Bay on the European side and Fil-Burun on the Asia Minor side and contains 5 coastal works on the 3.5 km long and 3 to 1 km wide stretch on the Rumelian side, namely the Rumeli-Feneri-Kalesst Fort and the Fort one battery, the Tapas-Vurun battery, the Gharibdsche fort, the high-lying Vöjük-Liman fort with a total of 97 guns, and on the Anatolian side three, namely the modern Anadoli-Feneri-Kalessi fort, the Poiras battery and the modern Fil-Burun fort a total of 64 guns.

The second group of fortifications, with the most important works, extends as far as the Böjükderebai and covers the only 570–740 m wide section of the fairway; In addition to the old, half-ruined Genoese castles Numeli-Kawak and Anadoli-Kawak, there are eight works with at least 198, but probably more, guns; Among these works, the new Numeli-Kawak battery with six heavy rifled guns, the Tali-Tabia fort with 30 smooth guns in a very good position just above sea level, the Dikili battery and the Mezar fort are particularly noteworthy on the European side -Vurun; on the Asian side the old Fort Anadoli-Kawak with eleven Krupp guns from 15 to 28 cm caliber, the new Fort Iuscha, the old giant castle with 8 Krupp guns and the very modern Fort Madschiar-Kalessi , the most important coastal work of the whole of B., with 30 Krupp cannons of 15 to 28 cm caliber, which are 8 m above sea level.

In the third section between Bo'zükdere and Therapia are the Fort Alti-Agatsch and the modern batteries of Therapia- and Kiridj-Burun, which enfilade the Kawak pass 4 km away with long-range guns. This pass between Rumeli and Anadoli Kawak is the most important point of defense; it is to be closed with three mine barriers in the war.

The innermost line of defense, the fourth group of coastal works, lies in the narrow (only 670 in wide) pass between the 14th century, modernized fixed castles Rumeli-Hissar and Anadoli-Hissar, each of which has around 20 guns , but has room for roughly double the number. A mine barrier is also to be laid between these works, but the current here is quite strong, five to six nautical miles an hour, so that the mines, if they were drifting, could easily become dangerous for Constantinople. An undersea telegraph cable leads from Fort Rumeli-Hissar over the B. to Kandillü. All in all, no less than 534 artillery pieces, 304 on the European side and 230 on the Asia Minor side, are supposed to be installed in these coastal fortifications of the Bosporus, including 40 heavy Krupp cannons and 50 heavy mortars. The defense of the Bosporus towards the Sea of ​​Marmara is as good as unprepared; however, at Constantinople there are three coastal batteries which could be armed with 150 guns; These are the battery in front of the arsenal in Tophane with 18 cannons and 6 mortars (has space for 96 guns), also the battery on the northern height of the Seraglio Hill, which is intended for about 40 guns, and finally one on the Asian side in Ekutari Battery near the old Maiden's Tower, for 9-14 guns. But only the salute battery in Tophane - with 6 bronze cannons - is in a usable condition. "


Ship accidents

The Bosphorus is open to international shipping day and night. It is one of the world's busiest sea routes as it is the only connection between the Black Sea and the Mediterranean. Over the past 30 years, the size and number of ships passing through this difficult, crowded and potentially dangerous waterway has increased steadily. 5,500 tankers pass the Bosporus every year, transporting 2 million barrels of oil per day.

The ocean currents and darkness are the main causes of ship accidents in the narrow S-shaped channel, which is more like a river than an international waterway. The main accident areas are the two places where the ships have to make a sharp turn (80 ° near Yeniköy, 70 ° near Umuryeri ) - in the 2 km long and narrowest part of the Bosphorus. In total, the ships have to change course twelve times when crossing the Bosphorus. At the narrowest point ( Kandilli , 700 m narrow), the course must be changed by 45 °; the current here can be 7 to 8  knots . Because of the sharp changes in course in the narrow water, the view of the fairway is blocked and the oncoming ship traffic cannot be seen. With the kilometer-long braking distance of today's large tankers, predictive driving is impossible.

In addition, there is a brisk ferry traffic between the European and Asian sides of the metropolis of Istanbul, which crosses the fairway.

In most accidents, ships have lost their maneuverability while going with the current and having to maneuver through sharp turns. In the accidents that occurred during the night, there were on average twice as many victims as in the daytime accidents. From 1953 to 2002 there were 461 ship accidents in the Bosporus, most of which were collisions. Since the introduction of the Traffic Separation Scheme (TSS) in 1994, which was also approved by the International Maritime Organization , the number of ship collisions has dropped sharply. After that, there were only 82 incidents - mostly stranding or running aground. However, not all ships meet the criteria for the TSS - because of the type of ship, their size or their maneuverability. The Traffic Separation Scheme defines a traffic separation line between northbound and southbound traffic, precisely defined by coordinates.

The biggest oil spill occurred in 1994 when the Greek-Cypriot tanker Nassia collided with the unloaded freighter Shipbroker on its way from Russia to Italy with 56,000 t of crude oil on board - at the northern entrance to the Bosporus. 30 people were killed and 20,000 tons of crude oil ran into the Bosporus, where it burned for five days and caused environmental damage. The Bosphorus had to be closed. Over 200 ships were stowed.

As a consequence of the accidents and to relieve the passage, the Turkish government brought the idea into play in 2011 to build the Istanbul Canal at Silivri , 150 meters wide and around 50 kilometers long.

On April 7, 2018, the 225-meter-long freighter "Vitaspirit", which was no longer steerable due to engine failure and sailing under the Maltese flag, rammed the 18th century red wooden villa Hekimbaşı Salih Efendi near the Fatih-Sultan-Mehmet Bridge on the Asian side. The building was used for events and was badly damaged by the collision.

Ship passage

Satellite image of Istanbul with registered districts

The procedures for the ship passage of the Bosporus are regulated separately for the passages to the south and to the north in the regulations Bosphorus Passage Procedure (on which frequencies and at which positions the stations Turkeli Control Station , Kavak Pilot , Bosphorus Pilot and Istanbul Control Station are called must and at which points position reports must be sent). The first contact must be made by the ship 30  NM before entering the Bosporus - 30 NM before the Turkeli lighthouse when approaching from the north, 30 NM before Haydarpasa Break Water when approaching from the south . Permission to drive through must be obtained by radio from the Traffic Control Center (German traffic control center ).

Sailing ships with a water displacement of over 500 t must submit a sailing plan at least 24 hours before the passage.

Turkish ships over 150 m in length are required to take a pilot on board for the passage of the Bosporus . There is no compulsory pilotage for the other transit shipping traffic, but is strongly recommended by the Turkish authorities. Ships with pilots on board have priority when entering the Bosporus.

Between 5:30 p.m. and 7:30 a.m. (night) only one ship with a total length of more than 250 m will be permitted to pass through the Bosporus (in the order in which it arrives at the Bosphorus entrance). During this time, tankers are only allowed to pass if they are accompanied by a tug. Otherwise they have to wait until the next daylight breaks.

Ships with a total length of more than 200 m or a draft of more than 15 m are recommended to pass through during the day.

For ships with dangerous goods, the passage is blocked in some places as long as a ship with similar dangerous goods is in oncoming traffic.

The ship's radar must be switched on for views below 2 NM . With visibility below 1 NM, ships with dangerous goods and large ships are not allowed to enter the Bosporus. If the visibility is less than 0.5 NM, traffic is stopped in both directions.

Ships are not allowed to cross the Bosporus on the tow of another ship unless they are being pulled by a tug.

The normal speed must not exceed 10 knots, unless it is necessary for the purpose of adequate steering - with prior approval. The distance to the ship in front must not be less than 1600 yards. The following ships must be informed before reducing your own speed.

Panoramic view of the Bosphorus from Topkapı Palace


Bridges and tunnels

Yavuz Sultan Selim Bridge, in the background the entrance to the Black Sea
Fatih Sultan Mehmet Bridge - the middle of the three Bosporus bridges

Three suspension bridges cross the Bosphorus, the Bridge of the Martyrs of July 15 (1973), the Fatih Sultan Mehmet Bridge (1988) and the Yavuz Sultan Selim Bridge (2016). The suspension bridges connect Europe with Asia.

All of them are multi-lane for road traffic and are subject to tolls when approaching the Asian side. The Yavuz Sultan Selim Bridge also has a double-track railway line. In October 2013, a railway tunnel was opened under the Bosporus, which connects the European side of Istanbul with the Asian side. The project is known under the name Marmaray .

At the southern end of the Bosporus, construction work on the Avrasya Tüp Tüneli ( Eurasia Tunnel ) began in February 2011 . This was opened on December 20, 2016 and is the first road tunnel under the Bosporus. It connects the western ( Kennedy Caddesi ) and the eastern part ( Harem İskele Caddesi ) of the D100 expressway . In February 2015, another tunnel project as a road and rail link was announced.

Overhead line crossings

Overhead lines across the Bosporus

In 1954, at the level of the Arnavutköy districts in Europe and Kandilli in Asia, the first overhead line across the Bosporus with a 154 kV line was pulled.

In 1983 another overhead line for 420 kV was pulled across the Bosporus, which was followed in 1997 by a third overhead line crossing for four three-phase circuits of 420 kV each. The masts for this overhead line crossing are already designed for 800 kV. Since the passage height on the Bosporus is 73 m, the masts of this overhead line crossing must be very high. However, the mountainous topography benefits the line construction. The masts of the Bosphorus crossing, completed in 1997, tower 160 m high.

  • Geographic coordinates of the line crossings:

Kandili: 41 ° 4 '12.43 "N 29 ° 3' 52.82" E
Arnavutköy: 41 ° 4 '15.98 "N 29 ° 2' 24.60" E

Web links

Commons : Bosphorus  - collection of pictures, videos and audio files

Individual evidence

  1. Süddeutsche: Second Bosporus for ships. Retrieved January 24, 2013 .
  2. Handelsblatt: Erdogan wants to dig the second Bosporus for ships. Retrieved January 24, 2013 .
  3. Herodotus 4.87
  4. Turkey plans second Bosporus , source RIA Novosti , accessed on May 5, 2011.
  5. Cargo ship crashed into historic building on the Bosporus, April 8, 2018, accessed April 8, 2018.
  6. a b German-Turkish newspaper: Istanbul: drilling of the Eurasia tunnel completed . ( Memento of the original from December 8, 2015 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot /
  7. ^ Breakthrough in the Eurasia tunnel - "Welcome to Europe" . In: tunnel . Official organ of the STUVA . No. 6/2015 . Bauverlag, October 2015, ISSN  0722-6241 , p. 40–44 ( online - magazine text bilingual German / English).