Trier calls itself Germany's oldest city, and nobody in a position to argue has managed to win. The Romans founded Augusta Treverorum around 16 BC, and by the fourth century it was one of the largest cities in the western empire, an imperial residence with palaces, baths and a great amphitheatre. The Porta Nigra, a massive black stone city gate from the second century, still stands on the northern edge of the old centre, grim and perfectly preserved because a hermit and later a church used it in the Middle Ages. A short walk away the Basilica of Constantine, a vast brick hall that was once a throne room, has a ceiling over thirty metres above the floor.
There are baths, an amphitheatre that held perhaps twenty thousand, a Roman bridge pier still carrying traffic in the Moselle, and a medieval cathedral that is among the oldest in Germany. UNESCO listed the whole set in 1986. Karl Marx was born here in 1818, and a small museum in the house tells the story. The Hauptmarkt, a handsome market square with a cross and a fountain, is the place to sit with a coffee, and the Moselle wines are served in the cafés around it.
The Moselle Wine Route comes to an end here, a ride that follows the river through some of the steepest vineyards in the world. The slopes of slate hold some of Germany's best Riesling, with a delicate, mineral, lightly sweet character, and the road weaves along the river with castles, villages and endless rows of vines. It is a slow, scenic ride rather than a fast one, with bends that follow the water, tractors and cyclists in season, and dazzling views from the bends where the river loops tightly. Spring and autumn are the best seasons, though the harvest brings its own traffic.
With about a hundred thousand people, Trier has everything: fuel, restaurants, hotels and bike shops, so you can sort out the practicalities with ease. Traffic in the centre can be slow, and much of the old town is pedestrianised, so leave the bike in a car park and walk. Luxembourg is just across the border, only a short ride away, with cheaper fuel, if you need it. After a long day, a glass of Riesling and a plate of local ham makes a good ending.