After examining the Strait of Hormuz and Gibraltar, we turn our attention to another historic chokepoint: the Bosporus, which has commanded passage in and out of the Black Sea for more than 2,000 years.
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I’m not sure what “a gift of ten of every kind” is, but it sounds pretty good. This, Herodotus tells us, is what Mandrocles of Samos received after designing a bridge across the Bosporus for the Persian King Darius:
After this, Darius, being well content with his bridge of boats, made to Mandrocles the Samian a gift of ten of every kind; wherefrom Mandrocles took the firstfruits and therewith had a picture made showing the whole bridge of the Bosporus, and Darius sitting aloft on his throne and his army crossing; this he set up in the temple of Hera, with this inscription:
“This Picture Mandrocles to Here gives,
Where for ever his Achievement lives;
A Bridge of Boats o’er Bosp’rus’ fishful Flood
He built; Darius saw, and judg’d it good;
Thus for himself won Mandrocles a Crown,
And for his isle of Samos high Renown.”
The Bosporus, of course, is one of the two narrow passages (the other being the Dardanelles, on which we will focus next week) that connect the Black Sea and the Mediterranean. The Bosporus is the northernmost of the two straits, linking the Sea of Marmara and the Black Sea, which Herodotus called
… of all seas the most wonderful. Its length is eleven thousand one hundred furlongs, and its breadth, at the place where it is widest, three thousand three hundred. The channel at the entrance of this sea is four furlongs broad; and the length of the channel, the narrow neck called Bosporus, across which the bridge was thrown, is as much as an hundred and twenty furlongs.
A narrow waterway between two major bodies of water is the perfect location for a major city, and the Bosporus is no exception. At its southwestern end, the Thracians built a city called Lygos, which was followed by a Greek city called Byzantium, which was renamed Constantinople by the Romans and Istanbul by the Turks. You can see one of the earliest images of the city and the waterway that made it possible in this 1422 map of Constantinople by Cristoforo Buondelmonti:
And this 1572 map by Braun and Hogenberg:
It was impressive enough in 513 BCE for engineers to build a bridge across a body of water three-quarters of a kilometer wide. But Mandrocles’s feat was even more impressive than that because of the Bosporus’s unique qualities. The immense force of the water spilling from the Black Sea into the Sea of Marmara (and eventually the Aegean) creates a tricky “Devil’s Current” at the surface. But below, a countercurrent pushes heavier, saltier water from the Sea of Marmara north into the Black Sea. On top of all this, winds from the north made it very difficult for ships to move into the Black Sea. This is one reason why Byzantium was founded in the first place: it gave crews that were weary from fighting the winds and the currents a place to rest.
So Mandrocles’s bridge — constructed by tying together hundreds of ships and then laying a bridge over them — was, if it existed, quite impressive. It linked Asia and Europe (not that many people thought in those terms back then). It recreated conditions that had likely prevailed about 9,000 years ago, when the Bosporus had been a strip of land separating the Sea of Marmara from the Black Sea, which was then a freshwater lake. When the last Ice Age ended, water levels rose and overtopped the Bosporus, causing salty water to rush into the Black Sea (some historians contend that this was the event referred to in the many ancient flood narratives, including the Biblical one, that emerged from the region).
So that’s one role for the Bosporus — connection, a place where two major landmasses and two major bodies of water come together. However, for most of recorded history, the Bosporus has been a chokepoint, too.
As the Ottomans chipped away at the Byzantine Empire, they were faced with an impossible-seeming task: conquering the city of Constantinople, which was surrounded on three sides by water and on the fourth by nigh-impregnable walls. Ottoman Sultan Mehmet II built a giant fortress whose cannon looked out on the Bosporus. He gave his generals clear instructions designed to strangle Byzantine trade:
Do not allow ships sailing from the Hellespont [Dardanelles] to the Black Sea or from the Black Sea to the Hellespont, no matter under whose flag they may be sailing — Genoese, Venetian, Constantinopolitan, Kaffatinian, Trapezundian, Amisinian, Sinopean, or even under my own flag, and no matter what class they are — triremes, biremes, barques, or skiffs — to sail through without first lowering their sails and paying the customs duties; only after they have done so will you permit them to proceed on their way. Use the cannon to sink the ship that does not comply and submit.
When a Venetian ship tried to run the blockade, the Ottomans sank the ship and impaled its commander, the unfortunate Antonio Rizzo.
The Ottomans, in fact, built two fortresses to command the strait, Anadoluhisarı, built in the 1390s on the eastern side of the Bosporus:
And Rumelihisarı, built six decades later on the west to allow the Ottomans to completely control the strait:
Though many of the more modern depictions of these fortresses make them out to be lovely and majestic, they served a clear purpose: to demonstrate Ottoman control over shipping through the strait. This 1721 folio makes sure to show the cannon barrels bristling out at the ships sailing through the Bosporus. It must have been a little nerve-wracking to run this gauntlet even in peacetime:
And these 18th-century maps make it clear just how tight a squeeze the strait was, and how commanding a position Istanbul had over it:
Next to the Ottomans, the Bosporus was probably most important to Russia. The country’s only warm-water ports, which were on the Black Sea, were useful only if Russian ships could get out to the Mediterranean. From Peter the Great onward, Russian leaders schemed to keep the Bosporus open. The Crimean War of the 1850s was partially about Russian ambitions in the Bosporus; the Ottomans allowed British and French ships through the strait to fight against Russia.
Eventually, most world powers agreed to keep the Bosporus closed to warships during peacetime unless the Ottomans agreed.
After the Ottomans fell and the Cold War began, the Bosporus became less important. The Soviet Union had more ways to get its ships out to sea, and Turkey was not the world power that the Ottoman Empire had been. But one incident in 1946 illustrated the Bosporus’s significance even in the Cold War era.
When the Turkish ambassador to the United States, Mehmet Münir Ertegün, died in 1944, his body remained in the United States until the end of the Second World War. When it came time to return his body in 1946, Harry Truman decided to send his casket home in style. The ambassador’s body was sent back to Istanbul on the U.S.S. Missouri — recently back home from hosting the signing of the Japanese surrender on its decks. The Missouri sailed right up the Bosporus and saluted Ertegün with its guns:
The message was clear: Americans would sail through the Bosporus and the Soviets could not stop them. The straits still held symbolic power even in the nuclear age.
For most of the Cold War period, the Bosporus was calm. The 1936 Montreux Convention had given Turkey control of the strait and contained clear provisions: merchant ships could travel freely but Turkey could deny warships passage. This was largely academic; the region was free of naval conflict for many decades.
Starting in 1973, the Turks spanned the Bosporus several times with impressive suspension bridges, some of the largest in the world. It seemed like the strait would, as in Mandrocles’s day, be a connector rather than a chokepoint in a more peaceful world. But the peace did not last.
Four days after the Russian invasion of Ukraine in 2022, Turkey invoked the Montreux Convention for the first time since World War II, denying passage to warships moving in and out of the Black Sea. Control of the Bosporus was once again an important strategic asset, as it had been for much of the last 2,500 years.
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