Largest attendance for simultaneous rock concerts

The largest live audience for a simultaneous rock concert is an estimated one million people for Live 8 held at concert venues around the world in 10 cities, including London, Philadelphia, Paris, Berlin, Johannesburg, Rome and Moscow on 2 July 2005.

source bbc online: http://news.bbc.co.uk/1/hi/entertainment/music/4645823.stm

struggling to get reliable figures...