Aosta is one of the most legible Roman towns in the Alps: the grid of its streets, its walls, the Arch of Augustus and the Porta Praetoria still organise the modern city. Less visible, but more surprising, is the cryptoporticus that survives beneath the ground near the cathedral. It is a double gallery, two parallel barrel-vaulted corridors separated by a row of massive pillars, running on three sides of the sacred area of the forum. Half-buried, lit only by narrow openings at the top of the walls, it served to level the terrain and to support the terrace above, and it may also have been used for storage and for passage. Today it is an extraordinary space to film: the rhythm of the vaults, the texture of Roman masonry, the shafts of light in the darkness. Filmed in 4K, the programme uses it to reconstruct the plan and the ambition of Augusta Praetoria.
