London - The medals for the 2012 Olympic Games were locked up on Monday in a vault at the Tower of London, where Britain's Crown Jewels are kept under armed guard.The 4 700 gold, silver and bronze discs will not be seen in public again until they are hung around the necks of the winning athletes at the Games, which open in the British capital on July 27.London Games chief Sebastian Coe took the medals down to the vaults, where they will stay until they are due to be awarded."For an athlete, winning an Olympic or Paralympic medal represents the conclusion of thousands of hours of training and reaching the highest level in sport," said Coe, who is himself a two-time Olympic 1 500-metre gold medallist."The victory ceremonies then provide the moment they can truly celebrate their success."The medals were greeted by a fanfare, as the tower's Yeoman Warder guards - commonly known as Beefeaters - watched with 150 schoolchildren from east London.The first medals will be awarded on July 28, in the women's 10-metre air rifle and men's 10-metre air pistol events.The gold medals are not actually made of solid gold. They are in fact 92.5 percent silver and 1.34 percent gold, while the rest is copper.Metals used in the medals were mined in Mongolia and Utah in the United States.Featuring some of the world's largest diamonds, the Crown Jewels are used by the British monarch during coronations and other state functions. They have been kept at the tower since 1661.The imposing castle has stood in east London since the 11th century and has a famously grisly history.It was first used as a jail in 1 100 and went on to witness the imprisonment and execution of many political and religious prisoners until the 17th century.It returned to this role during the two World Wars, with several spies executed there between 1914 and 1916.Rudolf Hess, Adolf Hitler's Nazi deputy, was one of the last prisoners to be held at the tower in 1941.