Important colonial victory early in the American Revolution .
Two months after the battles of Lexington and Concord , more than 15,000 colonial troops assembled near Boston to prevent the British army from occupying several hills around the city. The colonists fortified Bunker Hill (originally Breed's Hill) across the Charles River from Boston. Though they withstood a cannonade from British ships in Boston Harbor on June 17, 1775, and fought off assaults by 2,300 British troops, they were eventually forced to retreat. British casualties (about 1,000) and the colonists' fierce resistance convinced the British that subduing the rebels would be difficult.