Police this morning blew up an old cannonball that a fisherman at Castle Island in Southie found.

Massachusetts State Police Bomb Squad, along with the U.S. Navy buried the cannonball, which may have dated to the Civil War, in a sand berm at Carson Beach to absorb the detonation. 

The device was most likely inert, according to State Police, but was detonated around noontime out of an abundance of caution.