Roman Monuments, Cathedral of St. Peter and Church of Our Lady in Trier UNESCO World Heritage Site

Trier was founded by the Romans in the late 1st century BC in the land of the Treveri and named Augusta Treverorum after Augustus and the tribe. By the 2nd century it was a major trading centre, and after 170 the northern city gate, the Porta Nigra, was built. The Moselle bridge and the Barbara Baths also date from the 1st and 2nd centuries.

Under the Tetrarchy of the late 3rd and early 4th centuries Trier was one of four capitals, and from 293 to 395 it was a residence of the Western Roman emperor. Its population reached about 75,000 in the 4th century, and under Constantine the Imperial Baths and the throne hall known as the Aula Palatina were built. The Cathedral of St Peter is counted among the oldest church buildings in the Western world.

After the Franks took the city in 459, the Archbishop of Trier became one of the seven electors of the Holy Roman Empire. From 1028 the Greek monk Simeon lived as a hermit in the ruined Porta Nigra, and between 1034 and 1042 Archbishop Poppo built a two-level church inside the gate. The Church of Our Lady is described as the earliest High Gothic church built outside France, and the group was inscribed in 1986.