Aula Palatina

Step through the door and listen first. Your footsteps carry a long way in here. A cough near the entrance reaches the far end a moment later, softened by the brick. The air is cool, even on a warm day. Ahead of you there is mostly empty space, rising to a flat ceiling high above. It takes a few seconds for your eyes to understand how big this room is, because almost nothing inside gives you a sense of scale.

This is the Aula Palatina, the palace hall of the Roman emperor Constantine. Today many people in Trier simply call it the Basilica. It was built in the early fourth century, around the year 310 CE. At that time Trier was called Augusta Treverorum, and it was one of the capitals of the western Roman Empire. Emperors lived here, governed from here, and received visitors in this very space.

The word basilica can mislead modern ears. Today it usually means a large church. For the Romans, a basilica was a public hall, a place for law courts, business, and ceremony. This building was not built as a church. It was a throne room. Its job was to make anyone who walked in feel small, and to make the emperor at the far end feel very large.

The numbers help. The interior runs roughly sixty-seven metres long and about twenty-seven metres wide. The ceiling sits about thirty-three metres above the floor. Here is the first surprise: there are no columns holding anything up. It is one single open room. Of all the rooms that survive from Roman antiquity, this is generally considered the largest hall without interior supports. You are standing inside a record that has held for about seventeen centuries.

Now look toward the far end, at the curved apse. That is where the emperor's throne once stood. Visitors would walk the full length of the hall toward him, with daylight pouring in from the sides. Some scholars point out that the windows in the apse are set a little smaller and lower than those along the walls. If that was deliberate, it was a trick of perspective. It would make the apse look deeper, and the figure seated there look even more distant and powerful.

The room you see today is plain. In Constantine's time, it was not. The walls were covered in marble panels, and the floor was laid with polished stone. The building was also warm. Hot air from furnaces moved under the floor and through channels in the walls. Romans called this system a hypocaust, an early form of central heating. In a northern city with cold, grey winters, that warmth was its own message about imperial comfort.

When you go back outside, walk along the long side walls and look closely at the brick. The bricks are thin and flat, laid in tight rows with thick lines of mortar. You will also see rows of small square holes. Those are scaffolding holes. Roman builders pushed wooden beams into them to support their platforms as the walls rose. They were never filled in. Here is the second surprise: the outside was originally covered in plaster, so the bare brick you see now was never meant to be seen.

The hall did not stay a throne room for long. As Roman power faded, the building passed into new hands. During the Middle Ages it served the rulers of the region, and later the archbishops of Trier, who were also powerful princes. The great windows were partly blocked. Towers and living quarters were attached. For centuries, the Roman hall was hidden inside a fortress and later a palace. Many people living in Trier would not have known what the structure really was.

That changed in the nineteenth century. By then, Trier belonged to Prussia. The Prussian king Friedrich Wilhelm the Fourth took a strong interest in the Roman building. He ordered the later additions on this side to be removed and the hall restored to something closer to its ancient form. In the 1850s, the hall became a Protestant church. It still serves that purpose today as the Church of the Redeemer, so you may find a service, a choir rehearsal, or an organ concert in progress.

Then came the Second World War. In 1944, during an air raid, the building caught fire. The roof and the nineteenth-century interior were destroyed. Only the massive Roman walls remained standing. After the war, the hall was rebuilt with a deliberately simple interior, and it was used again as a church in the 1950s. So when you look around, you are looking at Roman walls, a postwar roof, and almost nothing in between.

That plainness is worth a moment of attention. Without marble, paintings, or statues, the room is mostly about light and volume. On a bright day, sun moves across the floor through the two rows of tall windows. On a grey day, the light turns soft and even. Sit on one of the benches for a minute. Notice how the sounds of the city disappear once the doors close behind you.

Before you leave the area, turn toward the building attached to the side of the hall. That pink and white palace is the Electoral Palace, built centuries later for the archbishop-electors of Trier. Its light, decorative style is the opposite of the heavy Roman brick beside it. In front of it lies the palace garden, with lawns, flower beds, and statues. The garden is a good place to step back and see the full height of the Roman walls.

The hall is part of a group of Roman sites in Trier listed together as a UNESCO World Heritage Site. Within walking distance you can reach the Porta Nigra, the great Roman city gate, as well as the imperial baths and the amphitheatre. Few cities north of the Alps keep so much of their Roman past above ground. This hall is perhaps the clearest picture of what imperial power here really looked like.

As you walk away, look back once at the long brick wall and its rows of small dark holes. Somewhere in that wall are the marks of workers who set each brick by hand, for an emperor they may never have seen. The roof is new. The purpose has changed many times. But the walls are still standing where they placed them, and the light still falls through the same high windows.