Trier

Trier is **the oldest city in Germany** — founded by the Romans in **16 BC** as **Augusta Treverorum**, and continuously inhabited ever since. In the late third century it became more than a provincial town: the emperors made it a **capital of the western Roman Empire**, Constantine lived here, and its population reached some eighty thousand, making it one of the largest cities in Europe. From that period Trier retains **the greatest concentration of Roman remains north of the Alps**, nine of them jointly UNESCO-listed: the **Porta Nigra** — the vast black gate that survived because it was converted into a church — the **Imperial Baths**, the **amphitheatre**, and the **Basilica of Constantine**, whose single hall is the largest surviving column-free interior from the ancient world. Note: **Karl Marx** was also born in Trier, in 1818, and his house is a museum. Note: the city sits on the Luxembourg border, and its centre is entirely walkable.