Bosphorus is a natural strait and the world's narrowest used for international navigation, that 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.
The limits of the Bosphorus are defined as the connecting line between the lighthouses of Rumeli Feneri and Anadolu Feneri in the north, and between the Ahirkapi Feneri and the Kadikoy Inciburnu Feneri in the south. Between these limits its length is 32 km in the north to south direction, width varies between 700 - 3420 m, with a width of 3,329 m at the northern entrance and 2,826 m at the southern entrance; and depth is between 13 to 110 m, in midstream with an average of 65 m. Bosphorus Strait separates two continents, Europe & Asia, thus the European part from the Asian part of Istanbul. The Golden Horn is an estuary off the main strait that historically acted as a moat to protect Old Istanbul from attack, as well as providing a sheltered anchorage for the imperial navies of various empires until the 19th century, after which it became a historic neighbourhood at the heart of the city.
The surface current flows always from north to south; however, a strong counter current under the surface creates swirls and eddies.
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.
The name Bosporus comes from the Greek word Bosporos. Its etymology is from «bous», (means ox) and «poros» (means of passing a river, ford, ferry). The similar Ancient Greek word for passage, strait is «porthmos», thus meaning oxen passage, which could reflect the older history of the region. The ancient Greeks analysed it as ox-ford or shallow sea ox passage and associated it with the myth of Lo's travels after Zeus turned her into a heifer for her protection. It has also been thought to be a Thracian form of Phosphoros (light-bearing), an epithet of the goddess Hecate.
It is also said in myth that floating rocks known as the Symplegades (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.
Historically, the Bosphorus was also known as the Strait of Constantinople, or the Thracian Bosphorus, in order to distinguish it from the Cimmerian Bosporus in Crimea. These are expressed in Herodotus' Histories as Bosporus Thracius and Bosporus Thraciae, respectively. Other names by which the strait is referenced by Herodotus include Chalcedonian Bosporus (Bosporus Chalcedoniae, Bosporos tes Khalkedonies), or Mysian Bosporus (Bosporus Mysius).
Presently, the waterway is officially referred to in Turkish “Bogazici” (Within the Strait), more recently it's been called the Istanbul Bogazi (Istanbul Strait), perhaps to differentiate it from the Dardanelles (Hellespont), called the Canakkale Bogazi (Canakkale Strait).
The exact scientific cause for the formation of the Bosphorus remains the subject of debate among geologists. One of the more prominent theories is the Black Sea deluge.
Glacial meltwater had turned the Black and Caspian Seas into vast freshwater lakes, while sea levels remained lower worldwide. The fresh water lakes were emptying their waters into the Aegean Sea. As the glaciers retreated, rivers emptying into the Black Sea reduced their volume and found new outlets in the North Sea, and the water levels lowered through evaporation. Then, about 5600 BC, as sea levels rose, Ryan and Pitman from Columbia University suggest, the rising Mediterranean finally spilled over a rocky sill at the Bosporus. The event flooded of land and significantly expanded the Black Sea shoreline to the north and west.
Ryan and Pitman wrote: “Ten cubic miles (42 km3) of water poured through each day, two hundred times what flows over Niagara Falls…. The Bosporus flume roared and surged at full spate for at least three hundred days.
The review of sediments in the Black Sea in 2004 by a pan-European project was compatible with the conclusion of Pitman and Ryan. Calculations made by Mark Siddall predicted an underwater canyon that was actually found. Some have argued that the resulting massive flooding of the inhabited and probably farmed northern shores of the Black Sea is thought to be the historic basis for the flood stories found in the Epic of Gilgamesh and in the Bible in Book of Genesis, Chapters 6-9. On the other hand, there is also evidence for a flood of water going in the opposite direction, from the Black Sea into the Sea of Marmara around 7000 or 8000 BC.
As part of the only passage between the Black Sea and the Mediterranean, the Bosphorus has always been of great importance from a commercial and military point of view, and 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 Russian-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.
The strategic importance of the Bosphorus dates back millennia. 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 Bosphorus, then marched towards the Danube River. His army crossed the Bosphorus over an enormous bridge made by connecting Achaemenes Boats. This Bridge essentially connected the farthest geographic tip of Asia to Europe, encompassing at least some 1000 meters of open water if not more. Years later, a similar boat bridge would be constructed by Xerxes I on the Dardanelles (Hellespont) strait, during his invasion of Greece.
The Byzantines called the Bosphorus Stenon and most important troponins 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.
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 330 his new capital, Constantinople, conferring on it the name Nova Roma (New Rome). This city came to be known as the capital of the Eastern Roman Empire. Constantinople (City of Constantine) was the name by which the city became instead more widely known. This remained the principal official name of the city throughout the Byzantine period, and the most common name used for it in the West until the early 20th century when it became known as Istanbul.
On May 29, 1453 the city was conquered by the emerging Ottoman Empire. As the Ottoman Turks closed in on Constantinople, they constructed a fortification on each side of the strait, Anadoluhisarı (1393) on Asian shore and Rumelihisarı (1451) on European shore.
In modern times several international treaties have governed vessels using the waters. Following World War I, the 1920 Treaty of Sévres demilitarised 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 remilitarised the straits area. The reversion to this old regime was formalized under the Montreux Convention Regarding the Regime of the Turkish Straits of July 1936. That convention, which is still in practical force as of 2008, treats the straits as an international shipping lane, but Turkey does retain the right to restrict the naval traffic of non-Black Sea nations (such as Greece, a traditional enemy, or Algeria).
Two bridges cross the Bosporus. The first, the Bosphorus Bridge, is 1074 m long and was completed in 1973. The second, Fatih Sultan Mehmet (Bosphorus II) Bridge, is 1090 m long, and was completed in 1988, about 5 km north of the first bridge. Construction of a third suspension bridge, the Yavuz Sultan Selim Bridge, began on May 29, 2013; opening is planned for early 2017. The bridge is built near the northern end of the Bosphorus, between the villages of Garipce on the European side and Poyrazkoy on the Asian side. It is a 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.
Another crossing, Marmaray, is a 13.7 km-long undersea railway tunnel was completed 29 October 2013. Approximately 1,400 meters of the tunnel run under the strait, at a depth of about 55 meters.
The Eurasia Tunnel is a road tunnel between Kazlicesme and Goztepe, which construction has begun in February 2011 and is expected to open in December 2016.
The Eurasia Tunnel, the 5.4 km double-deck undersea structure with two lanes on each deck, will cross the Bosphorus beneath the seabed, with the aim to alleviate Istanbul’s traffic pressure. It is at about 1 km south of the undersea railway tunnel Marmaray. With this new route, the journey time between Kazlicesme and Goztepe will be shortened from 100 minutes to 15 minutes.
The Bosphorus Bridge, also called the First Bosphorus Bridge or simply the First Bridge is one of two suspension bridges spanning the Bosphorus Strait.
It is a gravity-anchored suspension bridge with steel towers and inclined hangers. It is 1,560 m long with a deck width of 33.40 m. The distance between the towers (main span) is 1,074 m and the total height of the towers is 165 m. The clearance of the bridge from sea level is 64 m.
Upon its completion in 1973, the Bosphorus Bridge was the fourth-longest suspension bridge span in the world, and the longest outside the United States. Currently, it is the 22nd-longest suspension bridge span in the world.
The Fatih Sultan Mehmet Bridge (Sultan Mehmed the Conqueror Bridge), also known as the Second Bosphorus Bridge is the second suspension bridge spanning the Bosphorus Strait.
When completed in 1988, it was the 5th-longest suspension bridge span in the world; today it is the 19th.
The Yavuz Sultan Selim Bridge is named in honour of Ottoman Sultan Selim I (c.1470–1520), who expanded the Ottoman Empire into the Middle East and North Africa in 1514–1517 and obtained the title of Caliph of Islam for the Ottoman dynasty after his conquest of Egypt in 1517.
The bridge is part of the projected 260 km long Northern Marmara Motorway. The 58.4 m wide bridge will be 2,164 m in length with a main span of 1,408 m. The main span of the bridge will be eighth-longest among suspension bridges in the world. The bridge will be a combined road-rail bridge carrying four motorway lanes and one railway line in each direction.
MUSEUMS & SITES OF ISTANBUL
♦ Bosphorus Strait - A natural strait that connects the Black Sea with the Sea of Marmara and separates Europe from Asia
♦ Beylerbeyi Palace - one of the most magnificent Ottoman coastal palaces built in 1865
♦ Dolmabahce Palace Museum - The 19th century glamorous palace of Ottoman Sultans
♦ Hagia Sophia of Istanbul - The Church of Holy Wisdom built in 535 by Emperor Justinian
♦ Hippodrome (Atmeydani) - The stadium of ancient Byzantium, which once could hold 100.000 spectators
♦ Topkapi Palace Museum - The former seating residence of Ottoman Sultans built between 1459 & 1465