Puente Romano, Mérida

Feel the stone under your feet first. It is granite, worn smooth in the middle and rougher at the edges. The surface is pale grey with flecks of darker mineral that catch the light. Below you, the Guadiana River moves slowly through reeds and small islands. Herons stand in the shallows. Swallows cut low over the water. Then look along the deck ahead. It runs straight, then bends gently, and keeps going for longer than you might expect.

You are standing on the Puente Romano, the Roman Bridge of Mérida. It is one of the longest bridges to survive from the Roman world. Its full length is close to eight hundred metres. Count the arches if you have patience, because there are around sixty of them. For roughly two thousand years, people, carts, armies and livestock have crossed the river here. For most of that time, it was the main way into the city from the south.

To understand why the bridge exists, start with the city itself. Mérida was founded in 25 BCE on the orders of the emperor Augustus. Its Latin name was Augusta Emerita. The word emerita refers to the emeriti, soldiers who had completed their service. Many of the first settlers were veterans of Rome's long wars in the north of the Iberian Peninsula. They received land here as a reward. A river crossing was essential from the very beginning.

The site was chosen with care. Here the Guadiana is wide but fairly shallow, and it is broken by islands and gravel bars. The engineers used this landscape. If you walk toward the middle of the bridge, you will notice the change in direction. The deck shifts its angle near a large island in the river. Two separate sections may once have met here. Historians still discuss exactly how the original structure was laid out.

Now lean over the parapet and look at the piers, the thick supports that hold up each arch. Many of them have a pointed upstream face. This shape splits the current and pushes debris to either side. Look higher, above some of the piers, and you may see small openings through the masonry. These are flood vents. When the river rises, water passes through them instead of pressing against solid stone. It is a simple idea, and it has kept the bridge standing.

The Guadiana does not always look this calm. In winter and spring it can rise fast and spread across the flat land on both banks. Floods have damaged the bridge many times. That is the first surprise for many visitors. Not every arch you see is Roman. Some were rebuilt in the Middle Ages, and others in later centuries. If you compare the arches closely, you will see differences in the size of the stones and the way they are cut.

The Roman masonry is the easiest part to recognise. Look for large granite blocks with a rough, bulging outer face and neat, flat edges where they meet. This style is called rustication. It makes a wall look heavy and strong, and it also saves time, because the mason only finishes the joints. Later repairs often use smaller, more regular stones. Each layer of repair shows a moment when the city decided this crossing was worth saving.

Here is the second surprise. The bridge kept working after the Roman Empire collapsed in the west. In the fifth century, the Visigoths, a Germanic people who ruled much of Hispania, controlled Mérida. An inscription from that period records a restoration of the bridge. It credits a local official and the bishop of the city. So even in a time often described as dark, someone organised the work, paid for stone, and repaired the crossing.

The bridge also belonged to a much longer road. Mérida stood on the Roman route that later became known as the Vía de la Plata, the Silver Way. It ran north and south through the west of the peninsula, linking cities, mines and markets. Over many centuries, merchants and pilgrims followed it. Today, walkers on the Camino de Santiago still use parts of this route. You may see one pass you with a scallop shell tied to a backpack.

At the city end of the bridge, look at the heavy walls rising beside the river. This is the Alcazaba, a fortress built in the ninth century, when Mérida was under Muslim rule. Its builders reused Roman and Visigothic stones in its walls. The fortress was placed here on purpose. Whoever held the Alcazaba could watch the bridge, control the gate, and decide who entered the city. The bridge and the fortress always worked together.

For centuries, all traffic used this deck — people on foot, mule trains, carriages, and eventually cars and lorries. Modern weight and vibration put new pressure on old stone. In the early 1990s, a new bridge opened downstream, designed by the Spanish architect Santiago Calatrava. You can see its long white arch from here. After that, the Roman Bridge was closed to vehicles. Now it belongs to walkers, cyclists, and people who simply stop to watch the river.

The bridge is part of something larger, too. In 1993, the archaeological ensemble of Mérida was added to the UNESCO World Heritage List. That ensemble includes the Roman theatre, the amphitheatre, aqueducts, temples and this crossing. Few cities in Europe keep so many Roman structures still standing within a short walk of each other. And this bridge is unusual among them, because it never stopped doing the job it was built for.

Take a moment before you move on. Notice the sound of your own steps, and the quiet that comes without traffic. Look down at the water sliding under the arches, through gaps that Roman engineers left open for it. Look back at the Alcazaba walls and the rooftops of the city behind them. When you walk off the bridge, you will follow the same line into Mérida that its first veterans took... two thousand years ago.