Doctor Who: 14 Cool Details James Moran Just Revealed About The Fires Of Pompeii
12. The Doctor Makes A Callback To A William Hartnell Story
At the start of the episode, Donna asks the Doctor if he's been to ancient Rome before. He replies "ages ago", and adds "that fire had nothing to do with me... well, a little bit".
As noted by Moran, this is a reference to the William Hartnell story, The Romans, which was first broadcast in 1965. In this serial, the Doctor accidentally sets fire to a map of Rome, which gives Emperor Nero the idea to burn the city to the ground.
This means that the Doctor inadvertently caused the Great Fire of Rome. Yikes.