Fall of Arcadia

The Fall of Arcadia was one of the last battles, theorised to be the actual final battle, of the Last Great Time War. The Doctor was on Arcadia, fighting on the front lines, and he witnessed the fall. He also watched as the Daleks fled from the planet. (REF: Doctor Who: The Encyclopedia) He later said that it would take him a long time to recover from it. (DW: Doomsday)