Today marks the third anniversary of the Boston Marathon bombings that killed three and injured 264 spectators.
The 120th running of the marathon is Monday (local time) and law enforcement officials say the recent terror attacks in Europe underscores the need for extra security.
There will be 30,000 people running the 42.195km route and 1 million spectators along the way. Backpacks have been banned and so have drones. There are drone detectors to alert authorities.
Also, four Massachusetts state police helicopters will be in the sky providing surveillance help.
It can scan for people on rooftops and zoom in on suspicious objects like unattended bags.
But no amount of preparation will be enough for police to let down their guard.