LONDON - Solving the last remaining riddle of the opening ceremony, seven teenagers were given the honour of lighting the Olympic cauldron in the symbolic start to the 2012 London Games.

The final torchbearers light the Olympic Cauldron during the opening ceremony of the London 2012 Olympic Games at the Olympic Stadium July 27, 2012. [Photo/Agencies]

The young athletes, each nominated by a renowned British Olympian, lit a single tiny flame each within a copper petal on the ground, which triggered the ignition of more than 200 petals. The petals then rose towards each other to form one flame, described as a flame of unity.  

The lighting of the cauldron holds huge symbolism within the opening ceremony as the flame burns above the stadium for the duration of the Games.

The arrival of the flickering torch into the darkened stadium carried by five-times Olympic champion Steve Redgrave was greeted by a huge roar, bringing to an end a 70-day, 8,000-mile journey around some of the most famous landmarks in Britain where it was cheered on by millions of people.

It had earlier been driven up the Thames in a speed boat by former England soccer captain David Beckham.

The seven chosen youngsters were Callum Airlie, Jordan Duckitt, Desiree Henry, Katie Kirk, Cameron MacRitchie, Aidan Reynolds and Adelle Tracey, aged between 16 and 19.  

The choice of teenagers for the final stage marks a change from recent Games where some of the world's most famous athletes have carried out the lighting.

Chinese gymnast Li Ning lit the cauldron in Beijing in 2008. Raised into the air by wires, he ran around the rim of the stadium roof before lighting a wick which carried the flame to the cauldron.

Windsurfer Nikolaos Kaklamanakis lit the cauldron in Athens in 2004, 400-metre runner Cathy Freeman walked through a circular pool of water to light it in Sydney in 2000 and boxer Muhammad Ali did the honours in Atlanta in 1996.