Giant Olympic rings were launched on to the River Thames today to mark 150 days until the start of the London Games.
The rings, standing at 11 metres (36ft) high and 25 metres (82ft) wide, are travelling on a barge in the centre of the city and will pass landmarks including Tower Bridge and Canary Wharf.
Mayor of London Boris Johnson, who will watch Tower Bridge open to allow the rings to pass underneath, also announced a programme of free cultural events today that will take place in London during this summer's Games.
There will be free cultural events in every borough, which will include a floating opera inspired by The Owl And The Pussycat to be staged on the city's canals.
The rings, which are coloured on one side and have white LED lights on the other, were originally intended to start their journey at Battersea Bridge but instead were unveiled at London Bridge, meaning that they missed going past the Houses of Parliament as planned.
A spokesman for the mayor of London's office said this was because of "various issues relating to tidal flows and the height of the river".
Announcing the programme of events, Mr 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. Wherever you are, you will feel a part of the 2012 celebrations and experience a summer like no other in one of the most exciting cities on earth."
The floating opera is to be devised by Monty Python star Terry Jones and composer Anne Dudley and will form part of Secrets: Hidden London, which will see organisations including the Royal Opera House and English National Ballet transform canals, lidos and other city sites.
Other cultural plans announced today included a large-scale interactive public artwork by Jeremy Deller, to appear at locations across the capital, and the creation of the London Pleasure Gardens at Pontoon Dock, east London.
Ruth Mackenzie, director of the London 2012 Festival, said: "London and the UK's creative industries are world-beating and the London 2012 Festival will show them off to the world.
"With millions of free tickets and opportunities to take part, Londoners and tourists will truly have a summer like no other, thanks to the partnership between the mayor's office and London 2012 Festival."
The Rings on the River are to go into storage until the start of the Olympics, when they will again appear on the Thames.