Porta Nigra, Trier · Wikimedia Commons (CC BY-SA)

Porta Nigra

GateGallia Belgica · Trier, GermanyBuilt 170 CE

Not standing in 117 CE

About

Some 7,200 sandstone blocks, the heaviest around six tonnes, were stacked without a drop of mortar and locked together with iron clamps. The gate rose about 170 CE as the northern entrance of the new city wall, so it postdates the 117 CE snapshot by half a century. Rusting clamps and weathering blackened the pale stone and earned it its medieval name. A Greek hermit later walled himself inside it, which is why demolition crews spared it.

What happened here

The gate is where a town shows itself and where it counts what comes in. Traffic is funnelled between towers into arched passages — the wide ones for carts, the narrow ones for people — and closed at night with timber leaves shod in iron. A customs post takes duty on goods; a clerk records what passes. The outward face is the decorated one, with an inscription naming the emperor and the town, because this is the first thing a visitor reads. Guards are usually the town's own watchmen rather than soldiers. Just outside, the tombs begin; just inside, the shops. In a town whose walls have long stopped mattering militarily, the gate is kept up anyway, for the look of the thing.

In ancient writing

Tacitus, Annals 3.42
Recounts the revolt of Julius Florus among the Treveri in 21 CE, naming the tribe whose later capital, Augusta Treverorum, this gate guarded.