More than 12,500 runners headed through London's historic parks to help raise money to preserve and maintain the green spaces.
The runners, which included top athletes, took part in the first Royal Parks Half Marathon on Sunday.
The route took in several tourist hotspots including Hyde Park Corner, Buckingham Palace and the London Eye.
The event was organised to raise money for the Royal Parks Foundation and more than 150 other charities.
The course travelled along the river to Embankment and up to Trafalgar square before going back through Green Park, Hyde Park and Kensington Gardens.
London mayor Boris Johnson said: "The Royal Parks Half Marathon is an excellent way to celebrate their (parks) historic and abiding role in London life and is an another great public sporting event to add to the calendar as we build up to the 2012 Games."
Organisers said the race, which began at 1000 BST, was environmentally friendly, with runners' shirts made from bamboo fibre and race medals from pine.
Celebrity runners include Ben Fogle, actor Ross Kemp and former decathlete Daley Thompson.
The Royal Parks Foundation helps preserve and maintain the parks.