Principal Roman city of northeast Gaul, first the capital of Treveri, a Celto-Germanic tribe. It became the chief city of the Roman province of Belgica in the 2nd century AD and was adopted by Constantius and Constantine in the 4th century AD as an imperial capital. The city's strategic position at a crossroads contributed to its rapid rise as a commercial and administrative center. Remains include an amphitheater (c 100 AD), Constantinian basilica, baths, and Porta Nigra (ornate late Roman gateway). Trier has more preserved Roman monuments than any other German city. A mint was in use from about 296 AD.