The Porta Nigra, the "Black Gate" of Trier, is the city's landmark and the best-preserved Roman city gate in Germany and north of the Alps. It has been a UNESCO World Heritage Site in Trier since 1986. The monumental double gate was built around 170 AD under Emperor Marcus Aurelius as the northern city gate of the Roman city of Augusta Treverorum. It was originally about 36 meters long, 22 meters deep, and almost 30 meters high, and consisted of around 7,200 stone blocks weighing up to seven tons. The Romans precisely placed the stones on top of each other without mortar and connected them with iron clamps. The name Porta Nigra, which translates as "Black Gate," dates back to the Middle Ages and refers to the dark discoloration of the sandstone. The Romans themselves probably named the gate after the places it led to, or possibly Porta Martis (Mart's Gate). A key reason for the Porta Nigra's excellent preservation is its use during the Middle Ages. In the 11th century, the Byzantine monk Simeon moved into the east tower, where he lived as a hermit. After his death in 1035, he was canonized, and the entire city gate was converted into a church complex (St. Simeon's Church), which prevented its demolition. It wasn't until Napoleon's reign that the church was dissolved in 1803, and the city gate's original Roman form was restored. Today, the Porta Nigra serves as a museum and central information center on the Roman city, offering digital tours and an impressive model of the ancient city. Trier residents often refer to the gate simply as "Porta" (pronounced: POCHTA ;-))