So many cities have underground places - tunnels, sewers, mines, quarries, half-finished underground railways and the chambers that a lava flow has left.
In Naples they mainly used their underground places to hide: from bombs, from people, from mudslides and once from the flow from a nearby mountain called Vesuvius. It was a breath so hot it boiled away brains and forced bones to crumple into a penitent's rest.
It may come again, this terrifying wind. Next to Vesuvius, beneath the waters of the bay, is one of the world's supervolcanoes known as the Phlegraean Fields. Like its little brother, this supervolcano is fed by a magma chamber, but this one is gigantic and in July 2016 Robin Andrews
reported that the bay of Naples was rising - something that may signal a catastrophic eruption...or not.
No wonder Alexander Armstrong and Dr Martin Scott in Invisible Italy
seemed anxious to make their visit to Naples a brief one. The saying, 'Go to Naples and Die', they explained, came about during the Grand Tour because it sometimes ended with Syphilis, but given the precarious location it could also turn out to be an aphorism too. In which case the results of an amazing project to completely scan the city in 3D
- revealing how its vast underground and underwater systems connect with the buildings above - could be more valuable than we know. It also makes me understand the attraction of one of those virtual reality headsets.