Undaunted by the Boston Marathon bombings, big crowds lined the route of London's mass road race on Sunday to cheer on around 36,000 runners, many of whom wore black ribbons to honor the dead and wounded.
Hundreds of extra police were deployed to secure the first race in the World Marathon Majors series since two explosions near the finish line of the Boston Marathon on Monday killed three people and wounded 176.
"The best ever! A lot of emotion because of the Boston marathon," said Nathan Comer, 38, catching his breath just after finishing his third London Marathon.
"The silence before the marathon was beautiful ... it just felt as if everyone was together," he said, referring to a 30-second silence held in honor of the Boston victims just before the start of the race.
One spectator held up a placard that read "Come on London, do it for Boston!" while some runners had the name of the U.S. city emblazoned on their vests, but despite these somber reminders the mood was overwhelmingly one of celebration.
Small children reached out to high-five runners as they went past, spectators cheered elite and anonymous runners with equal enthusiasm, and a brass band near the starting line jokingly complained the boisterous crowds were drowning out their music.
"It was incredible, the amount of support, people coming out from everywhere, just cheering the whole way. Unbelievable," said a breathless Mo Farah, Britain's 5,000 and 10,000-metre Olympic champion, after running the first half of the course.
Farah ran half the route to prepare for competing next year.
The 26-mile course starts in leafy Greenwich, crosses Tower Bridge, snakes through the Canary Wharf business district before heading to Big Ben and finally Buckingham Palace.
Prince Harry, grandson of Queen Elizabeth, waited at the finish line to hand out medals to the winners.
"It's fantastic, it's typically British," he told the BBC, referring to the large turnout along the marathon route.
"People have been saying they haven't seen crowds like this for eight years around the route, which is remarkable to see ... The way that Boston has dealt with it has been absolutely remarkable. It's never going to get anyone down here."
London's Metropolitan Police Service said it increased the number of officers on the streets by 40 percent to reassure the public and not in response to any specific threat. Sniffer dogs were out in force and bins had been removed from the course.
"The enhancement to policing, which will see several hundred additional officers on the streets, is intended to provide visible reassurance to the participants and spectators alike," the police said on their website.
Before the start of the men's elite and mass races, official commentator Geoff Wightman led the crowd in a tribute to Boston.
"This week the world marathon family was shocked and saddened by the events at the Boston Marathon," he said over loudspeakers.
"In a few moments a whistle will sound and we will join together in silence to remember our friends and colleagues for whom a day of joy turned into a day of sadness."
The packed ranks of competitors bowed their heads and stood silently for 30 seconds, then clapped and cheered when a second whistle marked the end of the tribute.
Moments later, the world's elite runners led off the race. Behind them came thousands of competitors chasing personal goals or raising money for charity, many running in fancy dress.
Unusual outfits included a two-person camel costume, a giant beer bottle, a rhino, two male brides and Admiral Lord Nelson.
There were emotional scenes at the finish line as participants thought of Boston, but also in some cases of the sad reasons behind their involvement.
"It's been emotional and the atmosphere is brilliant," said cancer sufferer Hayley Kalinins, whose husband and brother were running for her and for a cancer charity.
After an unusually long and harsh winter, the weather came through for the London Marathon which began under bright sunshine and a cloudless sky.
Kenya's Priscah Jeptoo won the women's race by a long distance while Ethiopia's Tsegaye Kebede snatched victory from Kenyan rival Emmanuel Mutai in the final kilometer, to huge cheers from Londoners packed along the majestic tree-lined Mall.
The organizers will donate 2 pounds per finisher to The One Fund Boston, set up to raise money for the victims. They estimate around 35,500 people will cross the line, meaning they are likely to raise at least 70,000 pounds ($107,000).
In the German city of Hamburg, which was staging its own marathon on Sunday, runners also wore ribbons and held a minute of silence for victims of the Boston bombings.