LOS ANGELES, CA (Catholic Online) - Christianity first arrived in Trier as early as the first century. The cathedral, also known as the Dom St. Peter, was built by Constantine, the first Christian emperor, over the palace of his mother Helena. Construction began in 326 AD, to celebrate the 20th anniversary of his reign.

After damage wrought in the 5th and 9th centuries, the surviving part of Constantine's church was enlarged with major additions in the Romanesque style in 1035. Gothic and Baroque touches were later added.

The Empress St. Helena, known for her pilgrimages to the Holy Land, reportedly brought back the Holy Robe of Christ from Jerusalem and entrusted it to her son's new church at Trier. The Holy Robe is the seamless garment said to be worn by Christ during the Crucifixion.

The Robe made its first appearance in written documents in the 12th century. In 1512, the Holy Robe was first displayed in Trier for a period of 23 days, during which more than 100,000 pilgrims came to venerate it.

The next year, a wooden balcony was built onto the west front of the cathedral in order to display the Holy Robe and the other Trier relics to crowds gathered in Cathedral Square. It has been periodically displayed since then, attracting ever-larger crowds.

The last display of the relic, for three weeks in 1933, drew two million pilgrims. In 1959, the relic was sealed in a splendid shrine in its own chapel, where it remains today.

The cathedral's interior combines a Romanesque structure with baroque decoration and Gothic vaulting and archways. It is laid out as a triple-nave, two-choir basilica with a transept and six towers.

For visitors to Trier, the cathedral's central attraction is the Holy Robe (Der Heilige Rock) of Christ. The relic is enshrined in a reliquary housed in the specially-built baroque Chapel of the Holy Robe, located behind the altar.