Waterloo was a town in Wallonia, Belgium. (AUDIO: The Curse of Davros)
Napoléon Bonaparte's French Empire was defeated in a battle there on 18 June 1815. It was a major turning point of the Napoleonic Wars. Both the Second Doctor and the Sixth Doctor were present there during the battle. (PROSE: World Game, AUDIO: The Curse of Davros) Hougemont was located in Waterloo, and was a site of heavy artillery bombardment during the battle. (AUDIO: The Curse of Davros)
In June 1816, Lord Byron possessed the skeletal remains of a 15th century human soldier from the Waterloo Battle of Morat, which he kept in Villa Diodati. (TV: The Haunting of Villa Diodati)
The Fourth Doctor told a Sontaran Marshal that he was having his Waterloo when the Doctor managed to block its invasion of a future Earth. (TV: The Sontaran Experiment)