In June of 1775, Revolutionary forces got word of a British plan to capture
high areas around Boston in an effort to squash the Colonial uprising. 
Colonial forces, made up of about 1,000 men from Connecticut and
Massachusetts marched to an area on the Charlestown peninsula to lay claim
to this area before British troops could get there.

Colonial leaders hoped to fortify an area called Bunker Hill.  So on the
night of June 16, 1775, Revolutionary forces marched to the Charlestown
peninsula to set up a fortified area, in anticipation of the British
advancement.