This map shows how the city of Pompeii and its buildings caused changes in the direction and temperature of the pyroclastic flows that entered Pompeii during the 79 AD eruption. Our results show that the presence of the city caused the flow to move in different directions, such as moving along roads and around city walls. The presence of the city also influenced the flow temperature. The flows were cooled in places, although not to temperatures that would be comfortable for humans sheltering in the remains of the city. Imagine being in front of a ground-hugging cloud, moving towards you at a hundred miles an hour or more, containing sand, rocks and bits of building, and (if that's not enough already) at a temperature of more than 100 ºC. Credit: Gurioli et al., 2005