Osman Gazi Bridge

Listen first. Over the water comes a low, steady hum. It is the sound of tyres on steel, carried across the bay on the wind. Salt hangs in the air, mixed with a faint smell of diesel from the ships below. Then lift your eyes. Two pale towers rise from the sea, and between them a long, gentle curve of cable holds a road high above the waves. This is the Osman Gazi Bridge, and it crosses the Gulf of Izmit.

The gulf is a long, narrow arm of the Sea of Marmara. It reaches deep inland, east toward the city of Izmit. For centuries this water was a barrier. Travellers heading south from Istanbul toward Bursa or Izmir had two choices. They could drive the long way around the head of the bay, through heavy industrial traffic. Or they could wait for a ferry. The bridge removed that choice. Today the crossing takes only a few minutes.

The bridge opened in 2016. It links the Dilovasi shore, near Gebze, on the northern side with the Altinova area of Yalova province on the southern side. It forms one part of a much larger project — a motorway that connects Istanbul with Izmir, on the Aegean coast. The bridge was the most difficult piece of that route. Everything else could be built on land. This part had to be built over open, deep water.

Here is the number that most visitors miss. The main span — the distance between the two towers — is 1,550 metres. That is more than one and a half kilometres of road with no support underneath it. When the bridge opened, very few suspension bridges anywhere on Earth had a longer central span. With its approach spans, the whole structure runs for more than two and a half kilometres from shore to shore.

So how does a road hang in the air? Look at the two main cables. They run from anchor blocks on each shore, up over the tops of the towers, and down again in that long curve. Each cable is not one solid rope. It is made of thousands of thin steel wires, bundled tightly together. Vertical cables, called hangers, drop from the main cables and hold the deck. The weight of the road travels up the hangers, into the main cables, and down through the towers into the seabed.

The towers themselves are around 250 metres tall. That is taller than most skyscrapers in Istanbul. Their foundations sit on the floor of the gulf, in deep water. Builders prepared the seabed and lowered huge concrete foundations into place. Workers then raised the steel towers section by section. Afterwards, the deck was lifted up from barges in large prefabricated pieces and attached to the hangers, one after another, until the two halves met in the middle.

Now for the second surprise. This bridge stands in one of the most active earthquake zones in Europe. The North Anatolian Fault, a major break in the Earth's crust, runs through this region. In 1999, a powerful earthquake struck near Izmit, just east of here. It killed many thousands of people, and this whole coastline still remembers it. The engineers designed the bridge with that history in mind. The structure must be able to move and flex during a strong earthquake without collapsing.

A suspension bridge has a natural advantage here. It is not rigid. The deck can swing a little, and the cables can stretch slightly. Special dampers and joints allow parts of the structure to shift against each other. Wind matters too. The deck has a streamlined, wing-like shape, so strong winds from the Marmara pass around it smoothly instead of pushing it into a dangerous wave. A Japanese engineering company with deep experience in earthquake-proof bridges led the construction.

The name has meaning too. Osman Gazi refers to Osman the First, the founder of the Ottoman dynasty, around the end of the thirteenth century. The word gazi was an honorary title for a warrior. His early state grew in this same region of northwestern Anatolia, not far from Bursa and Yalova. So the name connects a modern steel structure with the very beginnings of an empire that once ruled from these shores.

Take a moment to look at the coastline around you. The Gebze side is one of the most industrial areas in Turkey. You will see factories, cranes, ports and container yards along the water. Large cargo ships pass under the deck all day, because the gulf is a busy shipping lane. The bridge was built high enough for those ships to pass beneath it freely. Watch one go under, and the scale of the deck suddenly becomes clear.

The southern shore feels different. Around Altinova and Hersek, the land is flatter and greener. There is a lagoon on that side where water birds gather. Small fishing boats work close to shore. Before the bridge, car ferries carried drivers across this water, and the ferry routes were part of daily life for many families. Some older locals still talk about the long queues at the docks on summer weekends.

Pedestrians cannot walk across the bridge. It is a motorway, and the only way over is by vehicle. The best views come from the shore. On the Gebze side, the old fishing village of Eskihisar sits close by, with its small harbour and a Byzantine-era castle on the hill. From the waterfront, the bridge stretches across the horizon. In the evening, the lights along the deck and towers come on, and their reflection breaks into pieces on the water.

So stand here a little longer. Notice the wind on your face, coming off the Marmara. Watch the tiny cars moving across that thin line in the sky. Each one is saving an hour of driving around the bay. As you leave, look back once more. The two towers will stay on the horizon for a long time — a quiet, steady line of steel, holding two shores together above the moving sea.