1851 incident

The 1851 incident, was the name given by The Secret Lives of Monsters to the event in which the Cybermen attacked London in 1851. (TV: The Next Doctor, PROSE: The Secret Lives of Monsters)

The Eleventh Doctor theorised this event was later erased by a crack in time created by total event collapse, due to the apparent lack of memory of it. (TV: Flesh and Stone)