Thousands of participants are preparing to take part at this year’s Boston Marathon amid tight security following last year’s bombings.
In last year’s race two bombs exploded near the finish line, killing three people and wounding more than 260.
But the attack has not deterred runners from Monday’s event. More than 36,000 will start – 9,000 more than normal.
Half a million spectators are expected to turn out. They will pass through checkpoints and will not be allowed to bring rucksacks – only clear bags.
Never before has the marathon been run amid so many layers of security.
Protecting the 26.2 mile route has involved a massive mobilization of law enforcement agencies, including police units, bomb squads and Swat teams from other states.
The Boston police department has erected 8,000 steel barricades, 1,200 more than last year.
Massachusetts Governor Deval Patrick told CBS television on Sunday that the added security measures would assure a “very safe” atmosphere.
Runners and their families posed at the finish line on Sunday, determined to take part in the event.
Many people in the city have been wearing “Boston Strong” T-shirts.
Last year’s winner, Lelisa Desisa, returns to compete again. He has met several victims of the blast, calling them “an inspiration”.
The event will begin with a moment’s silence at the start line at 08:45.
Bombing suspect Dzhokhar Tsarnaev, 20, is due to stand trial in November. He has pleaded not guilty to 30 charges, including 17 that carry the death penalty.
Prosecutors allege that Dzhokhar Tsarnaev set off two pressure cooker bombs with his older brother Tamerlan, 26, who later died in a police shoot-out.
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