Giant Olympic rings are towed on The River Thames past the Royal Naval College at Greenwich on February 28, 2012 in London, England. With 150 days remaining before the start of the London 2012 games the Olympic rings, measuring 11 metres high by 25 metres wide, are being showcased on the river as Mayor of London Boris Johnson is announcing details of two new cultural programmes, which will be part of the London 2012 Festival, along with details of other cultural events being organised to celebrate the London 2012 Olympic and Paralympic Games. ©PETER MACDIARMID / GETTY IMAGES EUROPE / Getty Images/AFP

(LONDON-AFP) – Giant Olympic rings were launched on the River Thames in London on Tuesday to mark 150 days until the start of the 2012 Games.

The rings — 25 metres (82 feet) wide and 11 metres (36 feet) high — travelled on a barge along the Thames, which runs through the centre of the British capital, and were to pass such landmarks as Tower Bridge and Canary Wharf.

London Mayor Boris Johnson, who was due to open Tower Bridge to allow the rings to pass underneath, also announced a programme of free cultural events to accompany the Games.

Johnson said: “2012 is one of the most thrilling years in our city’s history and as we welcome the world, we have an unprecedented opportunity to showcase and strengthen London’s outstanding culture and creativity, which are a hugely important part of our economy.

“From museums to theatre, and music to design, we have a reputation that is second to none and London’s finest artists and organisations are producing an exceptional range of brand new cultural events that will add to the excitement of hosting the Games.

“We’re creating the biggest festival of outdoor arts ever to be seen in the capital, as well as fantastic new work that will throw new light on some of our city’s lesser-known landmarks and hidden gems.”

The rings on display on Tuesday will be back on the Thames at the start of the Olympics, which get underway on July 27.