Runners and spectators turned out in force for the 33rd London Marathon in a show of solidarity to the victims of the Boston bomb attacks.
Just six days after the two blasts, London Marathon runners wore black ribbons and observed a poignant 30-second silence to honour the victims.
Around 35,000 competitors started the London race, while thousands more lined the streets to cheer them on.
The number of police officers on duty for the Marathon had been boosted by 40% to provide reassurance in the wake of the atrocities according to Scotland Yard.
Geoff Wightman, the event commentator, said to the massed runners:
Marathon running is a global sport. It unites runners and supporters on every continent in pursuit of a common challenge and in the spirit of friendship and fellowship.
This week the world marathon family was shocked and saddened by the events at the Boston Marathon."
The 26.2-mile route was filled with runners of all ages and nationalities, with many wearing weird and wonderful fancy dress costumes, such as a beer bottle, wedding dress and horse attire.
Among the runners, Karl Hinett, from Tipton in West Midlands, has dedicated his life to raising money by taking on physical challenges, despite sustaining 37% burns to his hands, legs, arms and face when his Warriors tank received a direct hit by a petrol bomb in Iraq in 2005.
The crowds were amazing and the weather was great. And if anything, what I witnessed today, after Boston, it just truly shows that the marathon running community is unbroken.
The Prime Minister congratulated the "inspiring" runners following the event:
Congratulations to the inspiring runners in the #LondonMarathon - a fantastic showcase for the city
Ethiopian Tsegaye Kebede won the London Marathon men's elite race in a time of two hours, six minutes and four seconds, while Kenya's Priscah Jeptoo, 28, came first in the women's race, clocking a time of two hours, 20 minutes and 15 seconds.
Prince Harry, who made the presentation to the winning athletes, paid tribute to the "remarkable" way the people of Boston dealt with the atrocities.
The royal told the BBC that he had always planned on attending the London event despite the terror attack at the finish line of the US race:
It was never an option as far as I was concerned. Certainly everyone that was planning on coming is still here, no one's changed any plans - the volunteers, the security, everyone is here, nothing's changed.
The way that Boston has dealt with it has been absolutely remarkable.
Celebrities including singer Katherine Jenkins, reality TV star Amy Childs, and presenter Sian Williams also took part in the Marathon.
ITV News' International Editor Bill Neely, who completed the Marathon in three hours and 16 minutes, reflected on running the London Marathon after spending the past week in Boston reporting on the marathon bombings.
He told Sports Editor Steve Scott: "Whatever pain I feel at the minute, and everyone here, I think a lot of people were feeling at one...And part of the running community with the people of Boston."
More than 1,000 St John Ambulance volunteers, working with the London Ambulance Service and Virgin London Marathon medical teams, treated more than 5,000 runners and spectators at this year's London Marathon.
Most of the runners who needed treatment were suffering from cramp, sprains, exhaustion and vomiting, according to St John Ambulance London regional events manager Katherine Eaton.