State Police report that, after consultation with the Navy, their bomb squad blew it up, shortly before noon.
The thing could date back to the Civil War, but State Police say they didn't want to take any chances:
Some cannonballs are filled with powder. If so, still could be an explosive capability.
Bomb-squad members buried the cannonball under a sand berm before detonating it (Photo by State Police):
Boston Fire Department units staged at the McCormack Bathhouse just in case. Boston police officers helped keep pedestrians away. Local TV stations were asked to pull their helicopters at least a mile away.
Boom! Capt. Greland videoed the detonation: