English: The circular stairway is a modern addition that takes you to the different levels.

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This is the largest Roman city gate north of the Alps and has been designated a World Heritage Site.

Porta Nigra (Black Gate) dates back to a time (about 180 AD) when the Romans often erected public buildings of huge stone blocks.

The slabs were cut by bronze saws powered by mill wheels (some cutting traces are still visible) and put together without mortar. Instead, two stones each were held together horizontally by iron clamps whose bent ends were embedded in corresponding holes by molten lead.

The name Porta Nigra (Black Gate) originated in the Middle Ages due to the darkened color of its stone; the original Roman name has not been preserved