Constantine built big. The Aula Palatina, which the Romans called the basilica, was the throne hall of the emperor's palace in Trier in the early fourth century, and it is still the largest single-room space to survive from antiquity. It is a plain brick box nearly seventy metres long, about twenty-seven wide and thirty-three high, with a huge apse at the end and tall windows set in two rows, and when it was finished it must have been dazzling, with marble on the walls, mosaics on the floor and heating under the floor. An emperor sitting at one end would have appeared tiny to petitioners entering from the far end, which was the idea.
Trier was at that time one of the capitals of the Roman Empire, a residence of emperors in the fourth century, and Constantine himself lived here in the years before he became sole ruler. The city had a palace, baths, a circus, an amphitheatre and a vast wall, and the remains are among the finest outside Italy. UNESCO listed the Roman monuments of Trier in 1986. The basilica was later used as a palace by the archbishops, and in the nineteenth century it was restored as a Protestant church, the Church of the Redeemer, which is why the interior is so plain and bright, with just a modern altar and a large organ.
The acoustics are good and concerts are held there regularly, and the whitewashed walls give the space a clean, severe beauty. Entry is usually free outside services, and it can be quiet and still. Next door, the Electoral Palace, a pink rococo building with a formal garden, offers a pleasing contrast.
In practical terms, you are in the heart of the old city, so leave the bike at an edge car park and walk. Trier has all services, and a wide choice of cafés near the Konstantinplatz, with a hundred thousand people to support them. Beyond the city, the Moselle valley and the Eifel provide excellent riding, with winding roads, vineyards and forests.
Visit in spring or autumn, when the light on the brick is warm and the tourists are fewer, and try a glass of local Riesling.