The Roman city gate in Trier, Germany, recognized as the largest surviving Roman city gate north of the Alps, is the Porta Nigra.
Built from grey sandstone after about AD 170, the gate marked the northern entrance to Augusta Treverorum, the Roman city now called Trier. Its monumental design used two massive, projecting towers and paired passageways, reflecting the military architecture of the Roman Empire’s northern frontier.
The name Porta Nigra, meaning “Black Gate,” was coined in the Middle Ages because the stone had darkened. Its original Roman name is unknown. Unlike many ancient gates, it survived because it was incorporated into a medieval church and monastery complex associated with the hermit Simeon, who lived there in the eleventh century.
Napoleon ordered the medieval additions to be partly removed in 1802–1804, restoring much of the gate’s Roman appearance. The Porta Nigra is now part of Trier’s UNESCO World Heritage ensemble, which also includes the Roman cathedral and Church of Our Lady.