Members of the public walk towards Buckingham Palace following the Queen's Birthday Parade, 'Trooping the Colour' at Horse Guards Parade in London on June 11, 2011. The ceremony of Trooping the Colour is believed to have first been performed during the reign of King Charles II. In 1748, it was decided that the parade would be used to mark the official birthday of the Sovereign. More than 600 guardsmen and cavalry make up the parade, a celebration of the Sovereign's official birthday, although the Queen's actual birthday is on 21 April. AFP PHOTO/Leon Neal (Photo credit should read LEON NEAL/AFP/Getty Images)