Beneath the Place du Forum in Arles lies a remarkable Roman structure: a horseshoe-shaped gallery of underground vaulted corridors built in the first century BC as a subterranean foundation for the forum above. The cryptoporticus is damp, cool, and lit by small high windows — an eerie space that has survived remarkably well.
The purpose of the structure has been debated — storage, slave quarters, circulation space — but its scale is impressive: the two main galleries stretch for about 90 metres each. Entry is through the Museon Arlaten, and the combination ticket is worth it. As one of the better-preserved examples of this type of Roman architecture anywhere, it earns its UNESCO listing.