Yavuz Sultan Selim Bridge

Listen first. Out here, at the northern mouth of the Bosphorus, the wind carries salt from the Black Sea. Gulls hang over the water and drift sideways. Somewhere below, a fishing boat's engine knocks and fades. Then you lift your eyes. Two pale towers rise from the green hills on either shore, and between them a road hangs in the air, laced with steel cables that catch the light like harp strings.

This is the Yavuz Sultan Selim Bridge, the third bridge to cross the Bosphorus. It opened in 2016. The two older bridges sit further south, among the palaces and apartment blocks of the city. This one stands almost at the edge of Istanbul. To the north, the strait widens and opens into the Black Sea. You are looking at one of the last pieces of human engineering before open water.

It helps to picture the whole strait. The Bosphorus is a narrow channel of water, around thirty kilometres long. It divides Europe from Asia and links the Black Sea to the Sea of Marmara. For most of history, people crossed it by boat. The first bridge came only in the 1970s. The second followed in the late 1980s. By the 2010s, both were choked with traffic, and the city decided to build again, further north.

Now look at the shape of the structure itself, because it is unusual. Most large bridges follow one of two designs. A suspension bridge hangs its deck from long main cables draped between towers. A cable-stayed bridge runs straight, angled cables from the towers down to the deck. This bridge does both. Near each tower, fans of straight stay cables hold the deck. In the middle, vertical hangers drop from great curving main cables. Engineers call this a hybrid design.

The design came from a French team. The lead name is Michel Virlogeux, a bridge engineer known for the Millau Viaduct in southern France, the tall road bridge that crosses a deep valley on slender piers. Here, the challenge was different. The bridge had to carry heavy loads across a very long span of water, without any supports in the strait below. Ships of every size pass underneath, day and night.

And here is the first surprise. The bridge was built to carry trains as well as cars. Down the centre of the deck, between the lanes of road traffic, there is space for two railway tracks. That is one reason the deck is so wide — close to sixty metres across, which made it one of the widest bridges of its kind in the world when it opened. The railway, however, was planned for the future. For now, the deck carries road traffic.

The main span, the open stretch between the two towers, measures 1,408 metres. That is longer than most suspension bridges anywhere. The towers themselves rise more than three hundred metres, taller than many skyscrapers. They are made of concrete, and they lean very slightly in their profile, shaped like a tall, narrow letter A. On a hazy morning, their tops can seem to disappear into the low cloud coming off the sea.

The name carries history, and some controversy. Yavuz Sultan Selim was an Ottoman sultan of the early sixteenth century. The word "Yavuz" is often translated as "the Stern" or "the Grim". He expanded the empire into the Middle East and Egypt during a short, intense reign. Naming the bridge after him drew criticism from Turkey's Alevi community, a religious minority. Many Alevis remember Selim's campaigns as a time of persecution of their ancestors.

The second surprise is about timing. The ground was broken in 2013, on the anniversary of the Ottoman conquest of Constantinople in 1453. Symbolism matters in Istanbul. Every bridge, mosque, and square sits inside a long conversation about who built this city and who rules it. Even a modern motorway crossing was placed inside that story.

The bridge also changed the landscape around it. It is part of a new motorway that runs through the forests north of Istanbul. These forests help supply the city with fresh air and water. Environmental groups argued that the road and the new development it attracts would cut into that green belt. As you look at the hills on either side, you can see both things at once — thick woodland, and the clean scar of the highway entering it.

Yet the shores here still feel like villages. On the European side sits Garipçe, a small fishing village with a few seafood restaurants and the remains of an Ottoman fortress above the water. Across the strait, on the Asian side, lies Poyrazköy, with its own old defences. These forts were built to watch the entrance from the Black Sea. Today, they watch the bridge instead.

The bridge is closed to pedestrians, so the best way to see it is from a distance. Many visitors take a long Bosphorus boat trip north and look up as the deck passes overhead. Others climb to the ruins of Yoros Castle, above the village of Anadolu Kavağı on the Asian shore. From there, the bridge sits framed against the open sea. At sunset, the towers turn gold, and then the lights come on along the cables.

Take a moment now, wherever you are standing. Watch a cargo ship slide under the deck, small against the towers. Listen for the low hum of traffic high above, mixed with the slap of water against the rocks. Two continents, one channel of moving water, and a thin line of steel between them. As you turn to leave, look back once more... the strait keeps moving, and the bridge holds still.