Definition of Trier
- a city on the River Mosel in Rhineland-Palatinate, western Germany; population 103,500 (est. 2006). French name Trèves Established by a Germanic tribe, the Treveri, circa 400 bc, Trier is one of the oldest cities in Europe. It was a powerful archbishopric from 815 until the 18th century, but fell into decline after the French occupation in 1797.