Runners from around the world came together in London to tackle the 26.2-mile marathon course and show solidarity to Boston.
Up to 40,000 competitors stood with their heads bowed at the start line in Greenwich Park for 30 seconds of silence, remembering those who lost their lives and limbs in the US.
Many wore black ribbons to honour 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 killed three people and wounded 176.
Among the many famous faces taking part yesterday were mezzo-soprano Katherine Jenkins, shadow Chancellor Ed Balls, cricketer Andrew Strauss and Harry Judd from the band McFly. Kate McCann, whose daughter Madeleine has been missing for six years, took part to raise money for missing children.
Ethiopia's Tsegaye Kebede won the men's race, with Priscah Jeptoo of Kenya winning the women's.
The women's wheelchair race was won by Tatyana McFadden, the American completing an emotional double just six days after winning in Boston. "All our thoughts are still with Boston," she said.
David Weir, looking for a record seventh London title, could only finish fifth in the men's wheelchair race, won in a sprint finish by Australian Kurt Fearnley.
The most notable moment of drama came as the front-running men's wheelchair racers overtook the elite women, when Canadian wheelchair racer Josh Cassidy knocked over the women's Olympic gold medal winner, Tiki Gelana.
Cassidy said after the event: "One of these years a woman is going to have a leg broken, a career ruined. It's just not worth having this programme if the races are going to suffer."
In light of the events in Boston last week, 40% more police officers than last year were deployed along the course. No specific threat was received, and the event passed off entirely peacefully. Hundreds of thousands of Londoners lined the route, as they do every year, calling out the runners' names and drinking beers in the bright sunshine.
But only those on the first half of the course saw Great Britain's double Olympic long-distance champion Mo Farah, who dropped out after 13 miles, as he had planned to, before praising the crowd and saying the experience was good practice ahead of running the full race next year. He also pocketed a rumoured £500,000 from the race sponsor Virgin.