The first relay runner was Greeck open water swimming champion Spyros Gianniotis
The Olympic flame was lit in Ancient Olympia in Greece on Thursday, in a solemn ceremony filled with mystery and tradition that signals the final countdown to the start of this year's summer Games in London.
Actors in ancient Greek costume invoked the god Apollo in the ruins of the 2,600-year-old Temple of Hera, using a concave mirror to harness the sun's rays and kindle a flame on the torch for a relay that will take it around Greece and Britain.
Dignitaries at the ceremony included the president of the International Olympic Committee Jacques Rogge, as well as the head of the London organising committee, Sebastian Coe.
"We promise to protect the flame, to cherish its traditions and stage an uplifting torch relay of which we can be proud," Coe said in a speech, vowing the event would "lift the spirits and hopes of people across Britain and across the world".
After thanks to the god Apollo, "king of the sun and the idea of light", in the shadow of the Greek, British and Olympic flags, the flame was handed to the first relay runner, Greece's Liverpool-born open water swimming champion Spyros Gianniotis.
He then passed it to 19-year-old British boxer Alexander Loukos, whose father hails from the Greek island of Lesbos and grew up in the east London borough where the Olympic Stadium is situated.
Gianniotis said after the full rehearsal at the temple on Wednesday that the torch ceremony was "a very big moment" for him, adding: "It is very moving.
"I am trembling from the emotions. It is the highest honour for an athlete to do this."
The ceremony marks the start of a week-long torch relay, which will take it to five major Greek archaeological sites, including the Acropolis, before it arrives at the old Olympic stadium in Athens, site of the first modern Games in 1896.
A British delegation will receive the flame at a night-time ceremony on May 17.
The last flame-bearers in Greece will be the weight-lifter Pyrros Dimas and the Chinese gymnast Li Ning, who lit the cauldron at the last Olympics in Beijing in 2008.
The London Olympic Games torch will tour the United Kingdom and also visit the Republic of Ireland before it arrives at the Olympic Stadium in east London on July 27 to a worldwide television audience of billions.
The torch's route in Britain starts on May 19 at Land's End, the southernmost tip of England to begin an 8,000-mile (12,875-kilometre) journey.
From June 3-7, it will visit Northern Ireland and then the Republic of Ireland -- the only country outside the United Kingdom on the torch route.
The inclusion of the Republic of Ireland would have been unthinkable just a few years ago and shows the ever-closer ties between it and Northern Ireland, 14 years after a peace agreement largely ended three decades of sectarian strike in the north.
In mainland Britain, a soldier wounded in Afghanistan and a 100-year-old woman are among 7,300 people who will carry the torch, organisers have said.
Also among the torchbearers is Jim Redmond, the father of former British 400 metres runner Derek Redmond, who famously helped his injured son hobble across the line during the 1992 Barcelona Olympics.
The torch relay culminates on July 27 with the final leg from Hampton Court palace, the riverside former home of king Henry VIII, to the Olympic Stadium for the opening ceremony that day.
The torch is a reminder of the ancient Olympics, when a flame burned throughout the Games. The tradition was revived in 1936 for the Olympics in Berlin.
No overseas legs of the torch relay have been planned this time round after those before the Beijing Games were hit by widespread protests against China.