It is the oldest cathedral in Germany and the largest religious structure in Trier, notable for its long life span and grand design.

The central part of the nave was built of Roman brick in the early fourth century, resulting in a cathedral that was added onto gradually in different eras.

[4] According to certain sources, the cathedral was commissioned by Emperor Constantine the Great and built on top of a palace of Saint Helen, his mother.

Following the conversion of Constantine to Christianity, Bishop Maximin (329–346) is said to have coordinated the construction of a cathedral, which at the time was the grandest ensemble of ecclesiastical structures in the West outside Rome.

Archaeological research confirms that the current cathedral, as well as the adjacent cloisters and Church of Our Lady, is raised upon the foundations of ancient Roman buildings of Augusta Treverorum.

Throughout the centuries the church continued to be rebuilt and embellished, according to the fashion of the period with Gothic vaults, Renaissance sculptures and Baroque chapels, but the overall style of the building remains Romanesque with a Roman core.

The imposing westwork of Trier Cathedral consist of five symmetrical sections and is typical of Romanesque architecture under the Salian emperors (11th century).

[5] The Latin inscription above the clock on the tallest tower reads "NESCITIS QVA HORA DOMINVS VENIET" ("You do not know what time the Lord is coming").

The original Roman structure is difficult to read on the inside but its basic rectangular form may still be recognized in the three easternmost bays of the nave.

[6] A Baroque chapel for the relic of the Seamless robe of Jesus, recovered from the previous main altar in 1512, was added behind the east choir and is visible through an opening in the wall.

The west choir is also decorated in the style of the German Baroque, and so are the chapels of Our Lady and the Holy Sacrament (with the "Golden Gate", part of the former rood screen), and most of the altars in the church.