<P> The Siege of Boston (April 19, 1775--March 17, 1776) was the opening phase of the American Revolutionary War . New England militiamen prevented the movement by land of the British Army garrisoned in what was then the peninsular city of Boston, Massachusetts . Both sides had to deal with resource supply and personnel issues over the course of the siege . British resupply and reinforcement activities were limited to sea access . After eleven months of the siege, the British abandoned Boston by sailing to Nova Scotia . </P> <P> The siege began on April 19 after the Battles of Lexington and Concord, when the militia from surrounding Massachusetts communities blocked land access to Boston . The Continental Congress formed the Continental Army from the militia, with George Washington as its Commander in Chief . In June 1775, the British seized Bunker and Breed's Hills, from which the Continentals were preparing to bombard the city, but their casualties were heavy and their gains were insufficient to break the Continental Army's hold on land access to Boston . The Americans laid siege to the British - occupied city . Military actions during the remainder of the siege were limited to occasional raids, minor skirmishes, and sniper fire . </P> <P> In November 1775, Washington sent the 25 - year - old bookseller - turned - soldier Henry Knox to bring to Boston the heavy artillery that had been captured at Fort Ticonderoga . In a technically complex and demanding operation, Knox brought many cannons to the Boston area by January 1776 . In March 1776, these artillery fortified Dorchester Heights (which overlooked Boston and its harbor), thereby threatening the British supply lifeline . The British commander William Howe saw the British position as indefensible and withdrew the British forces in Boston to the British stronghold at Halifax, Nova Scotia, on March 17 (celebrated today as Evacuation Day). </P> <P> Prior to 1775, the British had imposed taxes and import duties on the American colonies, to which the inhabitants objected since they lacked British Parliamentary representation . In response to the Boston Tea Party and other acts of protest, 4,000 British troops under the command of General Thomas Gage were sent to occupy Boston and to pacify the restive Province of Massachusetts Bay . Parliament authorized Gage, among other actions, to disband the local provincial government (led by John Hancock and Samuel Adams). It was reformed into the Provincial Congress, and continued to meet . The Provincial Congress called for the organization of local militias and coordinated the accumulation of weapons and other military supplies . Under the terms of the Boston Port Act, Gage closed the Boston port, which caused much unemployment and discontent . </P>

What fort supplied the cannon used to relieve the siege of boston