The Roman city gate, the Porta Nigra, is both a Trier city landmark and a UNESCO World Heritage Site.
With this construction, the Roman Empire wanted to impress with both size and power. It's nearly 30 meters in height is made up from some six tones of sandstone held together without mortar. It is a UNESCO World Heritage Site and very much a landmark of Trier.
The Porta Nigra was built around 128 A.D. It was called the black gate, not because of its color, but rather because soldiers on their way to war would pass through it, making it a place of mourning. During the rule of Constantine the Great Trier briefly became a capital city of the Roman Empire. For centuries it was the biggest Roman settlement north of the Alps. These days you can still take a Roman experience tour of the city gate, where you can encounter "real Romans". Tour guides dressed as centurions take you on a trip back in time to the age when Roman ruled the world.