It lies in a valley between low vine-covered hills of red sandstone in the west of the state of Rhineland-Palatinate, near the border with Luxembourg and within the important Moselle wine region.

Trier was one of the four capitals of the Roman Empire during the Tetrarchy period in the late 3rd and early 4th centuries.

[9] 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.

[9] With an approximate population of 110,000, Trier is the fourth-largest city in its state, after Mainz, Ludwigshafen, and Koblenz.

Since the last pre-Christian centuries, members of the Celtic tribe of the Treveri settled in the area of today's Trier.

[11] The city of Trier derives its name from the later Latin locative in Trēverīs for earlier Augusta Treverorum.

German historian Johannes Aventinus also credited Trebeta with building settlements at Metz, Mainz, Basel, Strasbourg, Speyer and Worms.

However, it remained the seat of a governor and had state factories for the production of ballistae and armor and woolen uniforms for the troops, clothing for the civil service, and high-quality garments for the Court.

Northern Gaul was held by the Romans along a line (līmes) from north of Cologne to the coast at Boulogne through what is today southern Belgium until 460.

South of this line, Roman control was firm, as evidenced by the continuing operation of the imperial arms factory at Amiens.

In the 17th century, the Archbishops and Prince-Electors of Trier relocated their residence to Philippsburg Castle in Ehrenbreitstein, near Koblenz.

A session of the Reichstag was held in Trier in 1512, during which the demarcation of the Imperial Circles was definitively established.

The persecutions started in the diocese of Trier in 1581 and reached the city itself in 1587, where it was to lead to the death of about 368 people, and was as such perhaps the biggest mass execution in Europe in peacetime.

The exact number of people executed in all the witch hunts within the diocese has never been established; a total of 1,000 has been suggested but not confirmed.

After conquering Trier again in 1794 during the French Revolutionary Wars, France annexed the city and the electoral archbishopric was dissolved.

The university, dissolved in 1797, was restarted in the 1970s, while the Cathedral of Trier was reopened in 1974 after undergoing substantial and long-lasting renovations.

Trier sits in a hollow midway along the Moselle valley, with the most significant portion of the city on the east bank of the river.