Nonetheless, the gate was used as a town entrance for centuries until the end of the Roman era in Trier.

The gates stood at the ends of the two main streets of the Roman Trier, one of which led north-south and the other east-west.

In the early Middle Ages the Roman city gates were no longer used for their original function and their stones were taken and reused for other buildings.

To save it from further destruction, the Porta Nigra was transformed into two superimposed churches with identical floor plans.

On his visit to Trier in 1804, Napoleon ordered that the Porta Nigra be converted back to its Roman form.

It was designated as part of the Roman Monuments, Cathedral of St Peter and Church of Our Lady in Trier UNESCO World Heritage Site in 1986 because of its testimony to the influence of Trier in the Roman Empire and its unique architecture as both a city gate and a double church.

Its modern appearance goes back almost unchanged to the reconstruction ordered by Napoleon, with a crowning cornice and parapet on its top.

Air pollution, particularly the exhaust fumes of passing cars, continues to darken and damage its stones.

In summer, tours are offered by a guide costumed as a centurion[4] (a Roman army officer) in full armor.