Beginning at around 1pm on 24 August, Mount Vesuvius sent gas, volcanic ash, and pumice into the stratosphere for up to 20 hours. This was followed by a pyroclastic flow that carried gas and molten rock down from the volcano and which then buried the previously fallen ash.

Although the emperor Galerius had previously issued an Edict of Toleration towards Christians, the Edict of Milan went further by establishing religious freedom throughout the empire and granting Christians the right to practice their religion without interference or persecution.