Founded by the Celts in the late 4th century BC as "Treuorum" and conquered 300 years later by the Romans, who renamed it "Augusta Treverorum" ("The City of Augustus among the Treveri"), Trier is considered Germany's oldest city. It is also the oldest seat of a bishop north of the Alps. In the Middle Ages, the archbishop-elector of Trier was an important prince of the Church who controlled land from the French border to the Rhine. The archbishop-elector of Trier also had great significance as one of the seven electors of the Holy Roman Empire.