Thousands of runners took part in the London Marathon, many saying it had been an emotional experience to compete in the shadow of the bombings at the Boston marathon last week.
The race was preceded by a 30-second silence, heightening London's sense of solidarity with Boston.
There was warm applause as a loudspeaker announcement said Londoners and marathon runners had united in tribute to the dead.
Intense security was evident along the 26-mile route (42 km) which took in major London landmarks such as Tower Bridge and the Houses of Parliament, and ended at Buckingham Palace.
Hundreds of police were out in force, sniffer dogs checked untended bags for explosives, and everyone approaching the finishing line had to pass a security checkpoint.
A number of runners who completed the London course had taken part in the ill-fated Boston marathon six days earlier.