Fortification of Dorchester Heights
Part of theAmerican Revolutionary War
Detail of a 1775 map of Boston, with Dorchester Heights at the bottom right
Date March 4–5, 1776 Location Dorchester Heights andBoston area 42°19′58″N71°2′47″W / 42.33278°N 71.04639°W /42.33278; -71.04639 Result British forces evacuate Boston on March 17
Belligerents
United Colonies	Great Britain
Commanders and leaders
George Washington John Thomas	William Howe
Strength
2,000–6,000 on Dorchester Heights	10,000 in Boston

TheFortification of Dorchester Heights was a decisive action early in theAmerican Revolutionary War that precipitated the end of thesiege of Boston and the withdrawal of British troops from that city.

On March 4, 1776, troops from theContinental Army underGeorge Washington's command occupiedDorchester Heights, a series of low hills with a commanding view ofBoston and itsharbor, and mounted powerful cannons there threatening the city and the Navy ships in the harbor. GeneralWilliam Howe, commander of the British forces occupying Boston, planned an attack to dislodge them. However, a snowstorm prevented its execution, so Howe withdrew instead. British forces andLoyalists who had fled to the city during the siegeevacuated the city on March 17 and sailed to Halifax, Nova Scotia.

Thesiege of Boston began on April 19, 1775, in the aftermath of theBattles of Lexington and Concord, and Colonial militia surrounded the city of Boston.^[1]Benedict Arnold, a captain in the Connecticut militia, arrived with his troops to support the siege. He informed theMassachusetts Committee of Safety that cannons and other valuable military stores were stored at the lightly defendedFort Ticonderoga inNew York, and proposed its capture. On May 3, the Committee gave Arnold a colonel's commission and authorized him to raise troops and lead a mission to capture the fort.^[2] Arnold,Ethan Allen, theGreen Mountain Boys, and militia forces from Connecticut and western Massachusettscaptured the fort and all of its armaments on May 10.^[3]

George Washington took command of the army outside Boston in July 1775, and ColonelHenry Knox raised the idea of bringing the cannons from Ticonderoga to the siege. Washington gave Knox the assignment of transporting weapons from Ticonderoga to Cambridge. Knox went to Ticonderoga in November 1775 and moved 60 tons^[4] of cannons and other armaments by boat, horse, and ox-drawn sledges along poor-quality roads, across two semi-frozen rivers, and through the forests and swamps of the sparsely inhabitedBerkshires to the Boston area.^[5][6] Historian Victor Brooks has called Knox'ssuccessful effort "one of the most stupendous feats of logistics" of the entire war.^[7]

The British military leadership headed by GeneralWilliam Howe had long been aware of the importance of theDorchester Heights and the heights ofCharlestown which had commanding views of Boston and its outer harbor. The harbor was vital to the British, as theRoyal Navy under AdmiralSamuel Graves (later under AdmiralMolyneux Shuldham)^[8] provided protection for the troops in Boston, as well as transportation of supplies to the besieged city. The British agreed on June 15 to the plan of seizing both of these heights, beginning with those in Dorchester, which had a better view of the harbor than the Charlestown hills.^[9] It was the leaking of this plan that precipitated events leading to theBattle of Bunker Hill.^[10]

Neither the British nor the Americans had the daring to take and fortify the heights, but both armies knew of its strategic importance in the war.^[11] Washington took command of the siege in July 1775, and he considered taking the unoccupied Dorchester Heights but rejected the idea, feeling that the army was not ready to deal with the likely British attack on the position.^[12] The subject of an attempt on the heights was again discussed in early February 1776, but the localCommittee of Safety believed that the British troop strength was too high, and important military supplies like gunpowder were too low to warrant action at that time.^[13] By the end of February, Knox had arrived with the cannon from Ticonderoga, as had additional supplies of powder and shells.^[14] Washington decided that the time was right to act.

Washington first placed some of the heavy cannons from Ticonderoga atLechmere's Point and Cobble Hill inCambridge and on Lamb's Dam in Roxbury.^[15] As a diversion against the planned move on the Dorchester Heights, he ordered these batteries to open fire on the town on the night of March 2; the British returned fire without significant casualties on either side. These cannonades were repeated on the night of March 3, while preparations continued for taking the heights.^[16]

On the night of March 4, the batteries opened fire again, but this time the fire was accompanied by action.^[17] This cannonade was continued on three successive nights, while the Americans made preparations to implement a plan devised byRufus Putnam to break the long siege.^[18][19][20] The American objective was to get cannon onto Dorchester Heights and fortify the position. However, the ground was frozen, so digging was impossible. Putnam had been a millwright, and he devised a plan using chandeliers (heavy timbers, 10 feet long, used as frames) andfascines. These were prefabricated out of sight of the British.^[18][19][20]

GeneralJohn Thomas,John Goddard, and about 2,500 troops quietly marched to the top of Dorchester Heights, hauling artillery, tools, and other military materials that had just arrived from Fort Ticonderoga to create the prefabricated fortifications and cannon placements. Hay bales were placed between the path taken by the troops and the harbor in order to muffle the sounds of the activity. Throughout the night, these troops labored at hauling cannon and building the parapet overlooking the town and the harbor. General Washington was present to provide moral support and encouragement, reminding them that March 5 was the sixth anniversary of theBoston Massacre.^[21] By 4 a.m., they had constructed fortifications that were proof against small arms andgrapeshot. Work continued on the positions, with troops cutting down trees and constructingabbatis to impede any British assault on the works.^[17] The outside of the works also included rock-filled barrels that could be rolled down the hill at attacking troops.^{[22][18][19][20]}

Washington anticipated that General Howe and his troops would either flee or try to take the hill,^[24] an action that would have probably been reminiscent of theBattle of Bunker Hill, which was a disaster for the British.^[25] If Howe decided to launch an attack on the heights, Washington planned to launch an attack against the city from Cambridge. As part of the preparations, he readied two floating batteries and boats sufficient to carry almost 3,000 troops.^[26] Washington's judgment of Howe's options was accurate; they were exactly the options that Howe considered.

British General Howe looked over from Boston the next morning and remarked that "the rebels have done more in one night than my whole army would have done in a month." He did not know what had been going on in the woods just six miles from his army.

Admiral Shuldham, commander of the British fleet, declared that the fleet was in danger unless the position on the heights was taken. Howe and his staff then determined to contest the occupation of the heights and made plans for an assault, preparing to send 2,400 men under cover of darkness to attack the position.^[27] Washington was notified of British movements and increased the forces on the heights until there were nearly 6,000 men on the Dorchester lines.^[28] However, a snow storm began late on March 5 and halted any chance of a battle for several days.^[29] By the time that the storm subsided, Howe reconsidered launching an attack, reasoning that preserving the army for battle elsewhere was of higher value than attempting to hold Boston.^[30]

On March 8, intermediaries delivered an unsigned paper^[31] informing Washington that the city would not be burned to the ground if Howe's troops were allowed to leave unmolested.^[32] The British forces departed Boston by sea on March 17 and sailed toHalifax, Nova Scotia, taking with them more than 1,000Loyalist civilians.^[33]

The fortifications on the Heights were maintained through the end of the war, and then abandoned. During theWar of 1812, the Heights were refortified and occupied against potential British invasion. Following that war, the fortifications were completely abandoned, and, in the later years of the 19th century, the Dorchester hills were used as a source of fill forBoston's expanding coastline.^[34]

In 1902, following revived interest in the local history, theDorchester Heights Monument was constructed on the (remaining) high ground in what is nowSouth Boston.^[34] The large Irish population in the area was also instrumental in having March 17 (which is alsoSaint Patrick's Day) named as theEvacuation Day holiday inSuffolk County, Massachusetts, which includes the city of Boston.^[35][36]

TheDorchester Heights National Historic Site was added to theNational Register of Historic Places in 1966, and in 1978 came under the administration of theNational Park Service as part ofBoston National Historical Park.^[34]

• 1776 in the United States
• Battles of the Boston campaign
• Battles involving Great Britain
• Battles involving the United States
• 18th century in Boston
• 1776 in the Province of Massachusetts Bay
• South Boston
• Battles of the American Revolutionary War in Massachusetts

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