500 was a number.
The First Doctor was in possession of a Five Hundred Year Diary by the time of his renewal into the Second Doctor. (TV: The Power of the Daleks) Shortly before he himself regenerated, the Second Doctor gave his age as a "tender" 500. (COMIC: The Brotherhood)
Gger was 500 light-years from Earth. (PROSE: Listen - The Stars)
The Master warned the Doctor and his companion, Emma, to prepare themselves for "five hundred miles of fear and faeces!" (TV: The Curse of Fatal Death)
Floor 500 was the top floor of Satellite Five. (TV: The Long Game, Bad Wolf, The Parting of the Ways)
