The city of Trier contains more significant Roman buildings than any other other place north of the Alps. It was designated a World Heritage site by UNESCO in 1981, in recognition of its rich Roman heritage and also because it has two very early Christian church buildings.
The Porta Nigra (Black Gate) was one of four gates built around 180 to 200 c.e. as part of the defenses of the city. Protecting the city from the north, the structure was built from gray sandstone, which by the Middle Ages had blackened to earn the name of Porta Nigra. Trier was an important crossing point over the River Moselle and the gates provided a necessary defensive shield around the site.
At more than 98 feet (30 m) in height, the Porta Nigra consisted of two four-story flanking towers with an entrance of two 23-foot- (7-m-) high carriageways for the passage of traffic. Within the building was a small courtyard. The large sandstone blocks were not held together by mortar but rested one on top of the other, pinned by iron clamps and rods. Although Trier’s three other gates were dismantled for house-building purposes during the Middle Ages, the Porta Nigra survived this fate because of the presence of a Greek monk, Simeon, who had lived a hermitlike existence within the building. After his death, a church was built within the Porta Nigra to honor his memory, with the courtyard acting as the nave. Despite some modifications, the original Roman structure remained essentially intact.
In 1802 Trier came under French control and, at the order of Napoleon, the church was dissolved and the Porta Nigra carefully restored as a Roman ruin. Despite the ravages of time and various marauders, the fortified gate remains an impressive sight, the largest such structure north of the Alps, and an eloquent reminder of Rome ’s imperial past.