Vasco da Gama Bridge

Stand at the edge of the water here and listen. There is a low, steady hum coming off the river. It is the sound of tyres on concrete, thousands of them, carried across the Tagus by the wind. The air smells of salt and wet mud, because this is not quite river and not quite sea. It is an estuary, wide and shallow, and stretching across it, further than your eye can comfortably follow, is the Vasco da Gama Bridge.

From where you stand, near Sacavém and the northern edge of Lisbon, the bridge does not look like a single structure. It looks like a line drawn across the water. It runs low and almost flat for most of its length, then rises near this shore into two tall towers hung with cables. On a hazy day, the far end simply disappears. The south bank, around Montijo and Alcochete, can be very hard to see at all.

Here is the first thing most visitors do not realise. This is the longest bridge in the European Union. The crossing itself runs for more than twelve kilometres. If you include the viaducts and access roads on both banks, the whole structure stretches for around seventeen kilometres. That is longer than many city centres are wide. Drivers who cross it for the first time often say it feels less like a bridge and more like driving over the sea.

The bridge opened in 1998, and the timing was not an accident. That year, Lisbon hosted a world exposition, known as Expo 98, on the land just south of here. The bridge was part of a much larger transformation of this side of the city. It also carried a symbolic name. In 1498, five hundred years earlier, the Portuguese navigator Vasco da Gama reached India by sea. The bridge was named for that anniversary.

Why did Lisbon need a second crossing at all? For decades, the only road bridge over the Tagus in the city was the 25 de Abril Bridge, the red suspension bridge further downstream, near the old centre. Traffic on it grew heavy and slow. Planners wanted another route that would take cars and lorries around the centre, not through it. This bridge was the answer, linking the north and south of the country without forcing everyone through central Lisbon.

Look now at the cable-stayed section, the part with the tall towers. In a cable-stayed bridge, the road deck hangs from straight cables that run directly down from the towers. This is different from a suspension bridge, where the deck hangs from a great curved cable. Here, the cables fan out like the ribs of a sail. The main span between the two towers is around 420 metres, wide enough for ships to pass beneath.

The second surprise is underground, or rather, under the water. Lisbon sits in an earthquake zone. In 1755, a massive earthquake, followed by a tsunami and fires, destroyed much of the city. The engineers who designed this bridge had that history firmly in mind. The structure was designed to resist an earthquake considerably stronger than the one of 1755. Its foundations go deep into the soft riverbed, far below the surface you can see.

The length of the bridge created another unusual challenge. Over a distance of many kilometres, the surface of the Earth is not flat. It curves, gently but measurably. Engineers on very long structures like this one must take that curve into account when they set out the piers. So, in a quiet way, this long straight line across the water actually follows the shape of the planet beneath it.

Now turn your attention to the estuary itself. The Tagus estuary is one of the most important wetlands in Portugal, and much of it is a protected nature reserve. In the colder months, it is a resting place for large numbers of migrating birds. Flocks of flamingos are often seen feeding in the shallow mudflats. Because the bridge crosses such a sensitive area, environmental concerns shaped its construction, and its impact on the wildlife was debated at the time.

On the ground around you, the story is about the city as much as the bridge. Sacavém sits where the small Trancão river meets the Tagus. For much of the twentieth century, this riverside was industrial, with warehouses, depots and refineries. The Expo project cleared and rebuilt large parts of the waterfront. Today, the green spaces of Parque do Tejo run along the shore near the bridge, with lawns, paths and benches facing the water.

If you walk south along the river, you reach Parque das Nações, the district built for Expo 98. Here you will find modern towers, riverside cafés, and the long promenade where locals jog, cycle and walk their dogs. A tall, slender tower near the water was built for the exposition and now houses a hotel. From almost every point along this promenade, the bridge fills the horizon, and it is one of the best places to see it.

The bridge changes with the light more than you might expect. In the early morning, mist often lies on the estuary, and the far end of the deck seems to float. In the middle of the day, the concrete looks pale and almost white against the blue water. At sunset, the towers and cables catch warm orange light. After dark, the lamps along the deck form a long string of points across the black water.

The bridge is built for motor traffic, so most people experience it from a car, a bus, or from the shore where you are now. And perhaps the shore is the best place for it. Take a moment here. Notice the hum of the traffic, the smell of the mudflats, the gulls overhead. Then look again at that long line across the water... five centuries after a voyage to India, Lisbon is still reaching across distances.