Giant Olympic rings were unveiled on Tower Bridge to mark the one month countdown to the London 2012 Games.
London 2012 chairman Lord Coe and mayor Boris Johnson were among the VIPs who watched as the rings were lowered into place on the central London landmark on the River Thames.
The rings, which weigh three tonnes and are 25 metres wide and 11.5 metres tall , cost £259,817 to produce and installing them is estimated to have cost £53,000.
All costs have been met from the £32 million Look and Celebration budget, which will be used to back free cultural events across London.
A light show, complete with beams of changing colours and intensity, is set to bring the rings to life tonight.
It will put into action Tower Bridge's new lighting system, involving 1,800 special energy-efficient LED lights, 2,000 metres of energy-efficient LED linear lights, 5,000 metres of cable and 1,000 junction boxes.
The Yorkshire-made rings are attached to a modular aluminium grid which is 17m by 22m. Together they weigh about 13 tonnes.
Each of London's famous bridges, from Hungerford Bridge to London Bridge, will be lit in "a dazzling display of colour" during the evenings, according to the mayor's office.
Giant mobile Olympic rings will travel up and down past famous waterfront landmarks.
The Agitos, the giant swirling symbol of the Paralympic movement, will replace the rings on Tower Bridge for the Paralympic Games.