On this day 250 years ago in Boston, the British Army awoke to discover that the Continental Army had erected two forts on Dorchester Heights within cannon shot of the British troops in Boston and the British Navy in Boston Harbor. The British commander General William Howe exclaimed

My God, these fellows have done more work in one night than my army could do in three months

General Washington had selected March 5 for the occupation of Dorchester Heights because it was the anniversary of the Boston Massacre and encouraged his troops to

Remember, it is the fifth of March, a day ever to be forgotten; avenge the death of your brethren

Because the American fortifications were at an elevated position on Dorchester Heights it was almost impossible for cannons on board the Royal Navy ships in the harbor to reach the forts, and most of the British artillery in Boston also could not reach the Continentals. For that reason, Howe immediately decided he had no choice but to capture the forts on Dorchester Heights and proceeded to put his men on board ships to be ferried to the base of Dorchester Heights. Fortunately for his men and the Continental Army, the weather intervened to prevent a repeat of the terrible bloodshed that had occurred in the previous year when the British charged the American fortifications on Breed’s Hill on the opposite side of Boston .

The diary of James Thacher, a Surgeon’s Mate in the Continental Army provides the best account of what happened on this day

At about four o’clock our regiment followed to the heights of Dorchester, as a relief party. On passing Dorchester Neck I observed a vast number of large bundles of screwed hay, arranged in a line next the enemy, to protect our troops from a raking fire, to which we should have been greatly exposed, while passing and repassing.

The carts were still in motion with materials ; some of them have made three or four trips. On the heights we found two forts in considerable forwardness, and sufficient for a defence against small arms and grape shot. The amount of labor performed during the night, considering the earth is frozen eighteen inches deep, is almost incredible. The enemy having discovered our works in the morning, commenced a tremendous cannonade from the forts in Boston, and from their shipping in the harbor. Cannon shot are continually rolling and rebounding over the hill ; and it is astonishing to observe how little our soldiers are terrified by them. During the forenoon we were in momentary expectation of witnessing an awful scene ; nothing less than the carnage of Breed’s hill battle was expected. The royal troops are perceived to be in motion, as if embarking to pass the harbor, and land on Dorchester shore, to attack our works. The hills and elevations in this vicinity are covered with spectators to witness deeds of horror in the expected conflict. His Excellency General Washington is present, animating and encouraging the soldiers, and they in return manifest their joy, and express a warm desire for the approach of the enemy ; each man knows his place, and is resolute to execute his duty.

Our breast works are strengthened, and among the means of defence are a great number of barrels, filled with stones and sand, arranged in front of our works; which are to be put in motion and made to roll down the hill, to break the ranks and legs of the assailants as they advance. These are the preparations for blood and slaughter! Gracious God! if it be determined in thy Providence that thousands of our fellow creatures shall this day be slain, let thy wrath be appeased, and in mercy grant, that victory be on the side of our suffering, bleeding, country.

The next day Thacher continued his journal to explain why the British called off their assault.

The anxious day has closed, and the enemy has failed to molest us. From appearances, however, there are strong reasons to suppose, that they have only postponed their meditated work till another day. It is presumed that the martial fire, which has been enkindled in the breasts of our soldiery, will not be extinguished during the night, and that they will not rest quietly under their disappointment. Early in the morning of the 6th, our regiment was relieved from its tour of duty, and I bade adieu to Dorchester heights, without being called to dress a single wound. Not more than two or three men were killed or wounded during the twenty four hours. Some of the British troops were seen to embark, and pass down towards the castle last evening, to be in readiness, it was supposed, in conjunction with others, to attack our works this morning; but a most violent storm came on in the night, and still continuing, obliges General Howe to abandon his enterprise, and thus has a kind Providence seen fit to frustrate a design, which must have been attended with immense slaughter and blood shed. General Howe must now be sensible of his exposed situation, and be convinced of the immediate necessity of evacuating the town of Boston, if he would prevent the sacrifice of his fleet and army.

Corporal Moses Sleeper was not part of the force that occupied Dorchester Heights but recorded in his diary what happened from his vantage point

Tuesday March th 5 last night about 8 O Clock the Canonading began & heald till Sunrise our people Intrenc’d upon Dorchester hills Last night one man killd with a Shell & two Wounded, belonging to a Party Comd by Leut burbank On Leach mores point this morning Our Regt. Was drawd out to go Into Boston Marchd with all Our Accutrements at 8 O Clock to the Grand Parade from thence was to embark In to the Boats Waited 4 hours for the motion of the Enemy & finding they were not Comeing out we Were Dismisd about 4 OClock

Wednesday March th 6 Last nigh a verry heavy Gale of Wind the wind at So West Cleard of this Morning

Sources: https://www.nps.gov/articles/000/revolutionary-war-diary-of-moses-sleeper.htm; https://historicaldigression.com/2026/03/05/witness-to-the-occupation-of-dorchester-heights-march-5-1776/; https://revolutionarywar.us/campaigns/1774-1776-boston-campaign/; https://www.nps.gov/articles/000/fortifying-dorchester-heights.htm#_ftn3; https://www.history.com/this-day-in-history/March-4/american-forces-occupy-dorchester-heights; https://www.nps.gov/articles/000/fortifying-dorchester-heights.htm#_ftn3; https://www.nps.gov/articles/000/gen-thomas-and-son-at-dohe.htm; https://www.hmdb.org/m.asp?m=26921; Fiore, Jordan D. & Susan E. Schruth, “The Noble Train of Artillery”, 200 Years Ago and Today, Commonwealth of Massachusetts Bicentennial Commission (1976) at p. 21

This weekend and next week in 2026, the National Park Service has sponsored multiple events to commemorate the occupation of Dorchester Heights and the subsequent Evacuation of Boston by the British https://home.nps.gov/articles/000/evacuation-day-250.htm