BOSTON - Tens of thousands of runners, cheered by a multitude of spectators, have set off through the streets of Boston to reclaim the world's oldest marathon from the fear left by last year's deadly twin bombing.
More than 3500 police, double the size of the force last year, and multiple government security agencies are keeping watch to prevent any replay of the ghastly carnage that visited the race on April 15, 2013 when two explosive devices tore through the crowds at the finish line.
Three people were killed and 264 injured in a rain of shrapnel.
"We want to show that the runner spirit is very resilient, and strong. This year we come back more and better than ever," said Amby Burfoot, the 1968 winner who is running again at age 67 after being kept from finishing the 2013 race because of the attack.
"The people of Boston - they will be there twice as many, twice as loud," he said.
A moment of silence was observed at the starting line in Hopkinton, just before the first wave of runners set off on the 42km course through Boston.
Disabled participants in wheelchairs were the first to go, followed by the elite runners.
A clear blue sky, sunshine and cool weather greeted the participants - 36,000 runners from all over the world, 9,000 more than last year and near the record 38,708 on the marathon's centenary in 1996.
A series of draconian safety measures were imposed, including a "no backpack" rule.
The Chechen brothers who allegedly carried out the 2013 attack, Tamerlan and Dzhokhar Tsarnaev, hid pressure-cooker bombs in their backpacks.
"We've tried to strike a balance between enhanced security and preserving the family feel of this day," Massachusetts Governor Deval Patrick said.
Across the city, people could be seen wearing "Boston Strong" shirts, with banners bearing the mantra proudly displayed in stores, restaurants and hotels.
Hundreds of runners and onlookers stopped by a memorial - decorated with flowers and shoes - in honour of those who perished in the bombings.
"We will never forget them," read a sign by four crosses with the names of those killed - including a police officer allegedly gunned down when he crossed paths with the attackers during the city-wide hunt for the two brothers.
Last year's winner, Ethiopia's Lelisa Desisa, is among those returning to compete again.
The 24-year-old has met several victims of the attacks, calling them "an inspiration" and has said he will be running again to show that he has no fear.
Several former winners are also taking part on Monday, including America's Joan Benoit Samuelson, who won in 1979 and 1983.
Run every year since 1896, the Boston marathon is one of the six biggest foot races in the world and part of the prestigious World Marathon Majors circuit.
The Tsarnaev brothers were identified as perpetrators of the attacks within days thanks to footage from cameras and thousands of photographs.
Tamerlan, 26, was shot by police on April 19, 2013, after killing an officer and Dzhokhar, now 20, was captured and stands accused of 30 federal charges. He is awaiting trial and could face the death penalty if convicted.