The Boston Marathon returns Monday under a major security crackdown after last year's deadly bombings as a near record 35,660 runners get set to compete.
One million people are expected to line the route in a show of defiance and to honor the victims and survivors of the attacks that killed three people and wounded more than 260.
More than 3,500 police -- double the number in 2013 -- plus members of 60 different local, state and federal security agencies, will deploy to protect the race.
Organizers have drastically tightened security steps for participants and bags have been banned at the start in Hopkinton, along the course and at the finish line.
The Tsarnaev brothers, the presumed bombers, allegedly hid the explosive devices in backpacks. Glass bottles and large containers of any kind have also been banned.
On its eve, Massachusetts Governor Deval Patrick vowed the massive event would be "very safe."
"We're very alert. We're very prepared, and we're assuring people as much as we can that it'll be a fun day and a safe one," he told CBS's "Face the Nation" show on Sunday.
Boston Police Commissioner William Evans told reporters last week the goal was to make the marathon the great race it has always been.
"We're not going to scare people and make it look like it's an army camp. We have plenty of cameras, we have plenty of assets and I'm very confident in our officers," he said.
Many Bostonians and fans of the marathon, the world's oldest, see Monday as a chance to defy terrorism.
Heather Abbott, amputated below the knee, will be standing close to the starting line to applaud those who saved her life, Peter Riddle and Erin Chatham.
"I'll be watching Erin Chatham, who's the woman who initially found me on the ground, cross the finish line," Abbott told AFP.
"She's running the marathon for the first time, and Peter is as well, so I'm really excited to be with them that day."
This year, organizers widened the number of entries from 27,000 last year to 36,000, close to the record 38,708 who ran in 1996 on the centenary of the race.
There will be more than 35,660 runners, 5,330 of whom come from 70 countries outside the United States.
Last year's win by Ethiopia's Lelisa Desisa passed almost unnoticed in the aftermath of the attack.
He returns to Boston, one of the six biggest foot races in the world and part of the prestigious World Marathon Majors circuit.
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 how 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, and Amby Burfoot (1968), who last year failed to complete the race in the wake of the attacks.
Last Tuesday, Boston paid emotional homage to the victims, survivors and first responders, united in their determination to conquer the fear of last year.
Vice President Joe Biden led the tribute, calling the survivors an inspiration to people all over the world.
Monday's marathon, Biden said, would send a message to the rest of the world and "to the terrorists that we will never yield, we will never cower."
But in the evening, hundreds of people were evacuated and a 25-year-old man detained for questioning over two suspicious backpacks found near the finish line.
More than 300 media outlets and 1,800 journalists will be covering the marathon, according to the organizers, the Boston Athletic Association.
Authorities have also announced an economic impact of $175.8 million in the Boston region, the highest in the history of the marathon.
The record so far was the 1996 rendition of the race, which generated $172 million.
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.