In the morning of 24th August or October 79 AD, a mushroom-shaped cloud of gas and volcanic rock rose high in the air. A shower of burning cinders and rock fragments covered Pompeii. The Pompeians tried to take shelter in the houses or hoped to escape by walking on top of the layers of pumice stones. At the dawn of the following day, a high-temperature pyroclastic flow hit the city at high speed and filled all the spots not yet engulfed by other volcanic materials, so that anybody still in the city died at once of thermal shock. The bodies of these victims remained in the same position as when the pyroclastic flow hit them and, being covered by calcified layers of ash, the form of their bodies was preserved even after the biological material decomposed. Thanks to the method perfected by Giuseppe Fiorelli, since 1863 a little over a hundred casts have been made.