One by one, the visitors descend through a tight tunnel cut through volcanic rock into the damp foundations of the Teatro Romano buried beneath Herculaneum, with the weight of 2,000 years of city above them.
“This is a time machine,” the guide says, “and we are going back.” It is pitch black as film-maker Gianfranco Rosi’s camera finds torchlight catching the tourists’ transparent waterproof capes, making them appear like ghosts.