Dorchester Heights

Early in the American Revolutionary War, a pivotal moment came when the fortification of Dorchester Heights helped bring the siege of Boston to a close and forced British troops to abandon the city. On March 4, 1776, Continental Army soldiers under the command of George Washington took control of Dorchester Heights, a stretch of low hills offering a clear view over Boston and its harbor. There they positioned formidable cannons capable of striking both the city and the Navy vessels anchored in the harbor. William Howe, the general leading British forces in Boston, drew up plans for an assault meant to drive them from this position. A snowstorm, however, made carrying out the attack impossible, leading Howe to pull back rather than proceed. On March 17, British forces together with Loyalists who had sought refuge in the city throughout the siege departed by sea, setting sail for Halifax, Nova Scotia.

Background

When Lexington and Concord erupted into violence on April 19, 1775, colonial militia forces responded by encircling Boston, initiating what would become a prolonged siege of the city. Among those who joined this effort was Benedict Arnold, a Connecticut militia captain, who brought his men to reinforce the blockade. Arnold recognized an opportunity: he told the Massachusetts Committee of Safety about valuable cannons and military supplies sitting at Fort Ticonderoga in New York, a position that was poorly guarded, and he pushed for a plan to seize it. The Committee responded favorably, granting Arnold a colonel's commission on May 3 along with authorization to recruit soldiers for a mission to take the fort. Within a week, on May 10, Arnold joined forces with Ethan Allen, the Green Mountain Boys, and additional militia units from Connecticut and western Massachusetts to successfully seize the fort along with its entire weapons stockpile.

By July 1775, Washington had assumed command of the forces besieging Boston. It was around this time that Colonel Henry Knox suggested a bold solution: transport the captured Ticonderoga cannons all the way to the siege lines. Washington approved the plan and put Knox in charge of moving the weaponry from Ticonderoga to Cambridge. Setting out for Ticonderoga in November 1775, Knox faced the daunting task of relocating 60 tons of artillery and other military equipment. His journey required boats, horses, and ox-drawn sledges to haul the cargo over rough terrain, through two rivers that were only partially frozen, and across the isolated forests and swamplands of the Berkshires before finally reaching Boston. This remarkable achievement later prompted historian Victor Brooks to describe Knox's undertaking as one of the era's most impressive displays of military logistics, ranking it among the war's greatest feats of its kind.

Geography and strategy

General William Howe and the rest of the British command had for some time recognized how much control over Boston and its outer harbor depended on holding Dorchester Heights and the high ground at Charlestown. Keeping that harbor open mattered enormously to the British, since Admiral Samuel Graves, and later Admiral Molyneux Shuldham, relied on the Royal Navy to shield the garrison in Boston and to keep supplies flowing into the besieged town. On June 15 the British settled on a scheme to occupy both elevations, starting with Dorchester, whose vantage over the harbor surpassed what the Charlestown hills offered. News of this scheme leaked out, and that leak set in motion the chain of events that led to the Battle of Bunker Hill.

For a time neither side found the nerve to actually seize and fortify these heights, though both understood clearly what such ground could mean for the outcome of the war. When Washington assumed command of the siege in July 1775, he weighed the possibility of occupying the still-vacant Dorchester Heights, then set the idea aside, judging his forces unready to withstand the British counterattack such a move would likely provoke. The question came up again in early February 1776, but the Committee of Safety in the area concluded that British numbers remained too great and that essential supplies, gunpowder chief among them, were running too short to justify moving forward. Toward the end of February, however, Knox brought in the cannon hauled from Ticonderoga, and fresh stores of powder and shells arrived as well. With these resources at hand, Washington judged that the moment to act had finally come.

Fortification

Cannon hauled from Ticonderoga were the first pieces Washington positioned, distributed among Lechmere's Point, Cobble Hill in Cambridge, and Lamb's Dam in Roxbury. To draw attention away from the coming operation on Dorchester Heights, he had these positions bombard the town on the night of March 2, and the British answered with their own fire, with neither side suffering serious losses. The exchange happened again the following night, March 3, even as plans moved forward for seizing the heights.

When night fell on March 4, the guns fired once more, only this time actual movement accompanied the noise. The barrage went on for three nights running, giving cover to the Americans as they carried out a scheme that Rufus Putnam had devised for ending the prolonged siege. Their goal was to place artillery atop Dorchester Heights and dig in there. Frozen ground made excavation out of the question, though. Drawing on his background as a millwright, Putnam came up with a method involving chandeliers, ten-foot timber frameworks, along with fascines. Both were built away from British view before being brought to the site.

Roughly 2,500 men under General John Thomas and John Goddard climbed to the summit of Dorchester Heights under cover of darkness, dragging along artillery pieces, tools, and other equipment newly arrived from Fort Ticonderoga so they could assemble the prepared defenses and gun emplacements. Bales of hay lined the route between the marching troops and the harbor to keep the noise from carrying. Across the whole night, the men strained to move the cannon and raise a parapet looking down on both the town and the water below. Washington himself came to lend encouragement, pointing out to the men that March 5 marked six years since the Boston Massacre. By four in the morning, they had raised works strong enough to withstand small arms fire and grapeshot. The soldiers kept building afterward, felling trees to form abbatis that would slow any British push against the position. Barrels packed with rocks were also placed on the outer edges, ready to be sent rolling down onto attackers.

Washington guessed that Howe would either pull his forces out or attempt to storm the hill, a move likely to echo the costly defeat the British suffered at Bunker Hill. Should Howe choose to strike at the heights, Washington intended to counter with his own assault on the city, launched from Cambridge. To that end he had two floating batteries prepared along with enough boats to transport close to 3,000 men. His read on Howe turned out to be correct, since those were precisely the choices Howe weighed.

British reaction

When dawn broke over Boston, General Howe surveyed the scene and admitted that the rebels had accomplished more in a single night than his entire army could have managed in a month's time. What he had missed entirely was the labor unfolding in the woods a mere six miles from his position.

Rear Admiral Shuldham, who commanded the North American fleet, warned that leaving the heights in rebel hands put his ships at risk. This pushed Howe and his officers toward action: they resolved to challenge the occupation and drew up plans to send 2,400 troops under night's cover to storm the position. Word of these preparations reached Washington, who responded by swelling the ranks on the Dorchester lines to nearly 6,000 men. Nature intervened, though, as a snowstorm rolling in late on March 5 delayed any confrontation for days afterward. According to Shuldham, the winds that same evening were too fierce to ferry Howe's 2,000 soldiers across for an assault on the fortifications. Once the weather cleared, Howe had second thoughts about pressing forward, deciding that keeping his army intact for future engagements mattered more than clinging to Boston. Shuldham noted by March 8 that supplies would last only fourteen more days without fresh shipments, and he began loading cannon and equipment onto vessels bound for Halifax.

That same day, unnamed go-betweens brought Washington an unsigned message promising the city would be spared from burning if the British were permitted to withdraw without interference. Howe's forces evacuated Boston by water on March 17, setting sail for Halifax, Nova Scotia, and bringing along over a thousand Loyalist civilians in their company.

Legacy

The defensive works atop the Heights remained in place until the war's conclusion, after which they fell into disuse. When the War of 1812 raised fears of another British landing, the site was fortified once more and garrisoned as a precaution. Once that conflict ended, however, these defenses were left behind for good, and by the latter part of the 19th century, the hills of Dorchester were being carted away as fill to extend Boston's shoreline outward.

A renewed appreciation for the area's past led to the erection of the Dorchester Heights Monument in 1902, placed on whatever high ground still remained in what is today South Boston. The neighborhood's substantial Irish community played a key role in establishing March 17, a date shared with Saint Patrick's Day, as Evacuation Day, a holiday observed throughout Suffolk County, Massachusetts, home to the city of Boston.

Recognition on a national level came in 1966, when the Dorchester Heights National Historic Site earned a place on the National Register of Historic Places. Later, in 1978, oversight of the site passed to the National Park Service, folding it into Boston National Historical Park.