<P> The 2012 Summer Olympics , formally the Games of the XXX Olympiad and commonly known as London 2012 , was an international multi-sport event that was held from 27 July to 12 August 2012 in London , United Kingdom . The first event , the group stage in women 's football , began on 25 July at the Millennium Stadium in Cardiff , followed by the opening ceremonies on 27 July . 10,768 athletes from 204 National Olympic Committees ( NOCs ) participated . </P>
where was the summer olympics held in 2012
London