The British were marching toward Lexington and Concord because they wanted to seize and destroy arms and ammunition stockpiled by American militias in Concord. This march, on April 19, 1775, became known as the first battle of the American Revolution.
The British Army wanted to degrade the rebel militias' ability to fight, and to arrest the leaders of the sedition, Samuel Adams and John Hancock. Marching from Boston at around 2 a.m., the British soldiers encountered some light resistance from Colonial militias. In Concord, they searched the town for weapons, discovering cannons, ammunition and military provisions, which they destroyed or damaged beyond use. On the way back, the British troops encountered more militia forces that harried them as they withdrew to the Boston area. The British advance on Concord caused Paul Revere to make his famous ride to rouse the Colonial militiamen to fight the British.