After the Boston Tea Party in 1773, British troops quartered in the town of Boston using their warships to keep Boston harbor closed. These actions cut off trade, crippled the economy, and put colonists out of work. British soldiers and colonists, now living in proximity, frequently brawled in the streets and in the taverns. People who had never paid much attention to political affairs now became overt or secret supporters of one side or the other. Biased broadsides and newspaper reports fostered enmity. Tensions came to a head on April 18, 1775, when British General Thomas Gage, appointed royal governor of Massachusetts, sent 700 British soldiers to Lexington and Concord to confiscate arms and ammunition being accumulated by the colonists.

Some of the colonists, forewarned about British troop movements, were waiting on the Lexington Green when the British arrived the next morning. To this day no one knows for sure who fired first, but a shot rang out. The British soldiers fired a volley into the colonial militia, killing eight men and wounding 10. The British then moved on to Concord where minutemen drove back three British infantry units guarding Concord’s North Bridge. On their subsequent march back to Boston they were peppered by patriot snipers. By the time the redcoats reached Boston, they had suffered 273 casualties compared with fewer than 100 for the patriots.

Engravings in local newspapers and broadsides incorrectly reported that the British, after attacking Lexington and Concord, raided and pillaged property all the way back to Boston. That news enraged patriots throughout the colonies. Within 48 hours, militiamen from Connecticut, New Hampshire, and Massachusetts gathered in and around Cambridge, across the Charles River from Boston. The many differences that had separated the various colonies, including different religions, systems of government, and lifestyles, were set aside for a greater cause.

The Massachusetts Committee of Public Safety, headed by patriot leader Dr. Joseph Warren, selected Artemas Ward to take command of the volunteer soldiers around Boston. Ward, the senior general of the Massachusetts colonial army, reluctantly took command, but some groups of men remained under the control of their colonies’ militia company leaders. Slowly, however, these colonial armies placed themselves under Massachusetts’ command and became a New England army. By mid-June 1775, approximately 7,600 troops were camped in and around Cambridge.

While the patriots were mobilizing, General Gage tried to decide how best to deploy his 5,000 British regulars. He realized that whichever side could take control of the high ground of Charlestown, Roxbury Heights, and Dorchester Heights would have the advantage in a battle. The British army set forth a plan to occupy the hills around Boston by late June. Fortunately for the colonists, patriot leaders and the Massachusetts Committee of Public Safety learned of the plan and resolved that the colonial army should beat the British to the high ground by fortifying the hills of Charlestown.