Siege of Boston

April 19, 1775–March 17, 1776 — British Forces Trapped in Boston

The Siege of Boston started after the battles of April 19, 1775, and Massachusetts Militia followed British troops back to Boston. In the days that followed, militia from New Hampshire, Connecticut, and Rhode Island joined Massachusetts to confine the British to the city. The siege lasted from April 19, 1775, until March 17, 1776. It was part of the Boston Campaign and included the Battle of Bunker Hill and the Fortification of Dorchester Heights. It ended in an American victory when the British evacuated the city.

Thomas Gage

General Thomas Gage was in charge of the British forces in Boston prior to, and during most of the Siege of Boston. He was replaced by William Howe in October of 1775.

Siege of Boston Summary

The Siege of Boston —  also called the Battle of Boston — was a series of military operations between the American Colonies and Britain that took place in and around the city of Boston, Massachusetts, from April 19, 1775, to March 17, 1776.

On the morning of April 19, British troops engaged Massachusetts Minutemen and Militia at Lexington and Concord. As the British marched back to Boston, the militia followed, shooting at them along the way, inflicting heavy casualties. When the British finally returned to Boston, they took refuge on Bunker Hill while the militia surrounded the city and set up a siege.

The Massachusetts Provincial Congress asked the nearby colonies to send help and placed Artemas Ward in command of the militia, which was transformed into the New England Army of Observation.

British reinforcements arrived on May 25, and several skirmishes took place. Meanwhile, in Philadelphia, the Continental Congress set up the Continental Army with George Washington as Commander-in-Chief.

At the same time, the Battle of Bunker Hill took place in Boston. The British won the battle but suffered heavy casualties and the Americans gained a moral victory.

Washington arrived and took command of the army on July 3. The siege continued through the summer and fall.

In November, an expedition under the command of Henry Knox set out for Fort Ticonderoga. The purpose was to retrieve the cannons and artillery that had been captured at the Battle of Fort Ticonderoga and transport them to Boston. After Knox returned in January, the Americans used the guns to fortify positions around Boston, including Dorchester Heights, which overlooked the British ships in Boston Harbor.

The location gave the Americans a tactical advantage and the British decided to evacuate the city. On March 17, the British army, including Loyalists who wanted to leave Boston, sailed out of Boston Harbor, which ended the Siege of Boston.

Quick Facts About the Siege of Boston

  • Also Known As: The Siege of Boston is also known as the Battle of Boston.
  • Date Started: The Siege of Boston started on Wednesday, April 19, 1775.
  • Date Ended: The siege ended on Sunday, March 17, 1776.
  • Location: The siege took place in and around the city of Boston and Boston Harbor.
  • Campaign: The siege is considered to be part of the Boston Campaign of 1775–1776.
  • Who Won: The American Colonies won the Siege of Boston.
This illustration depicts the American camp at the Siege of Boston. Image Source: New York Public Library Digital Collections.

5 Things to Know About the Siege of Boston

  1. The Siege of Boston started after the Battle of Lexington and Concord when the Massachusetts Militia pinned British forces in Boston.
  2. The Siege of Boston, which began in 1775, ended when the British were forced out of the city in March 1776 by the Continental Army.
  3. Colonial soldiers won the Siege of Boston, even though they were poorly trained compared to the British. However, the colonial militia forces had spent a considerable amount of time preparing for hostilities with Britain. The British were surprised at how well the militia was organized and how well they fought.
  4. The Battle of Bunker Hill took place during the Siege of Boston. Artemas Ward was in command of the American militia forces and his army was referred to as the Army of Occupation.
  5. The Second Continental Congress reorganized the Army of Occupation and renamed it the Continental Army. George Washington was named Commander-In-Chief and replaced Ward.

What Happened at the Siege of Boston? — History and Important Events that Led to the British Evacuation of the City

Prelude to the Siege of Boston

British troops occupied most of Boston and were led by General Thomas Gage, commander-in-chief of the British forces. Gage had also been appointed Governor of Massachusetts by King George III. Gage had four regiments of British regulars under his command in Boston.

Around July 1, 1774, Admiral Samuel Graves arrived at Nantasket Roads, where he took command of the North American Station with orders to enforce the Boston Port Act, blockade Boston Harbor, support the British Army, and help Gage enforce the rest of the Coercive Acts.

The American Revolutionary War Begins — April 19, 1775

On the night of April 18, 1775, Gage sent British troops to Concord with the intent to destroy colonial military stores, and possibly to capture John Hancock and Samuel Adams, who were staying in Lexington with Reverend Jonas Clarke. On the road to Concord, the British Regulars were held up at Lexington by Massachusetts Minutemen who assembled on Lexington Green, under the command of John Parker. It was there, in the early hours of the morning of April 19th, that the first shots between British regulars and American militia were exchanged, and the American Revolutionary War began.

After the skirmishes in Lexington and Concord, the British marched back to Boston but were followed and harassed the entire way by the militia. When the British reached Boston, many of them camped on Bunker Hill, where they were protected by the guns of the warships sitting in Boston Harbor.

The Siege of Boston Begins — April 19

The news that war had broken out and that the British had attacked quickly spread. The neighboring colonies showed their support by sending troops. Rhode Island sent men under the command of Nathanael Greene. New Hampshire sent theirs under the command of Colonel John Stark. Connecticut also sent men under the command of Major General David Wooster, and two brigadier generals — Israel Putnam and Joseph Spencer.

Map of Boston in 1775, during the Siege. Image Source: Wikipedia.

The Massachusetts militia built a siege line around Boston and Charlestown, where the British were garrisoned. The line extended from Chelsea, North of Boston, to Roxbury, South of Boston.

On April 22, Gage moved his troops out of Charlestown into Boston, which left Charlestown, Bunker Hill, Breed’s Hill, and Dorchester Heights completely undefended.

The next day, April 23, the Massachusetts Provincial Congress voted in favor of calling more men to arms, and to place the Massachusetts Militia under the command of Artemas Ward.

The following were also named major generals (on various dates):

With Boston surrounded by militia from several colonies and the Port blockaded by the British, there were people who wanted out of the town — and others who wanted in. An agreement was reached between Gage and the Committee of Safety that opened the roads up, so people could come and go. However, the British were alarmed by the number of people — especially those considered rebels — who were leaving Boston. Gage’s subordinates believed those rebels had value as hostages. Gage reversed course and made it difficult for people to obtain the passes necessary to leave Boston.

At the same time, there were many Loyalists who went into Boston, looking for protection from the British forces. These Loyalists informed Gage of the number of the militia surrounding Boston. Gage decided to remain in a defensive position and awaited the arrival of reinforcements. Gage had fortifications erected at Barton’s Point to the Northwest, Copp’s Hill to the Northeast, and Fort Hill to the East, and South, across the passage to Roxbury. Despite the fortifications, the whole Western side of Boston, along with Boston Common and Beacon Hill, was left open to attack. In order to defend the West, Gage had a small fort erected on Beacon Hill.

Meanwhile, the militia surrounding Boston was trying to find a way to better organize themselves. The largest contingent of troops was the Massachusetts men, under the command of Artemas Ward. Ward’s authority came from the Provincial Congress of Massachusetts, which communicated with Ward through Dr. Joseph Warren, who was the head of the Committee of Safety. The commanders of the other militia groups agreed to submit to Ward as commander-in-chief, however, the chain of communication was lacking.

Although there were small skirmishes throughout the month of May, nothing substantial occurred until May 21. The British were in need of hay to feed their horses, so Gage sent an expedition to Grape Island to retrieve the hay that was needed. The militia responded by sending troops to engage the British. At first, the battle consisted of long-range shooting, but the militia was able to get a sloop from nearby Hingham and get to Grape Island. Once on land, they set fire to the barn where the hay was kept. Roughly 80 tons of hay went up in flames. After this, the militia began removing cattle, sheep, and hay from the islands around Boston.

British Reinforcements Arrive — May 25

On May 25, British Generals John Burgoyne, Henry Clinton, and William Howe arrived in Boston aboard the frigate, HMS Cerberus, along with reinforcements. The Cerberus was under the command of Captain John Chads.

Battle of Chelsea Creek — May 27

More skirmishes broke out on May 27 when Ward sent militia under the command of John Stark and Israel Putnam to capture livestock and seize British supplies on Hog Island and Noddle’s Island in Boston Harbor. A British schooner, HMS Diana, under the command of Lieutenant Thomas Graves, and a sloop opened fire on them. The schooner ran aground and was seized by the militia and burned. The operation was successful, as the militia was able to capture the livestock and provisions.

Gage Offers Pardons to All Rebels Except Hancock and Adams — June 12

On June 12, Gage issued a proclamation. The document, written by Burgoyne, offered pardons to all rebels except for Samuel Adams and John Hancock. The proclamation angered the colonists, who were outraged over the British attacks on Lexington and Concord. Now that reinforcements had arrived, Gage began to set a plan in motion to capture Dorchester Heights.

Birth of the United States Army — June 14–15

On June 14, the Second Continental Congress voted on and approved the formation of the Continental Army. This placed all the militia forces outside of Boston under the control of Congress and marked the birth of the United States Army. George Washington was named Commander-in-Chief of the Continental Army on June 15.

Militia Prepare to Seize Bunker Hill

That same day, the Committee of Safety in Boston, having learned of Gage’s plan to seize Dorchester Heights, advised the militia to seize Bunker Hill. Roughly 1,200 men were placed under the command of Colonel William Prescott. The goal of the expedition was to occupy Bunker Hill and build fortifications, which would overlook both Boston and the Charlestown Peninsula. Prescott and his men assembled on Cambridge Common on the night of June 16. From there, they marched towards Bunker Hill. Upon arrival, however, Prescott and his men chose to build their fortifications on Breed’s Hill, which was smaller than Bunker Hill and closer to Boston.

Battle of Bunker Hill — June 17

On June 17, British regulars under the command of Major General William Howe and Brigadier General Robert Pigot landed on the Charlestown Peninsula and marched to Breed’s Hill. As the British advanced, Prescott reportedly told his men, who were low on ammunition, “Don’t fire until you see the whites of their eyes.” When the British were close enough, the militia fired, sending the British into retreat.

The British regrouped and charged again, but were once again forced to retreat. However, when the British charged for the third time, Prescott’s men found themselves out of ammunition and were forced into hand-to-hand combat. The militia was outnumbered and was eventually forced to retreat. However, they had killed more than 200 British troops and wounded roughly 800 more. The American forces lost 100, including Dr. Joseph Warren, and had 300 wounded. Although the American forces lost their strategic position, the Battle of Bunker Hill boosted the morale of the militia, because they proved they could hold their own against the supposedly superior British regulars.

Painting of the death of Joseph Warren at the Battle of Bunker Hill by John Trumbull. Image Source: Wikipedia.

Washington Takes Command — July 3

Three weeks later, on July 2, Washington arrived in Watertown, Massachusetts. After meeting with the Massachusetts Provincial Congress, he traveled to Cambridge. On July 3, he took command of the Continental Army. Throughout the rest of the summer, Washington worked to organize the various militias into an Army and fortify and expand defenses around Boston.

The British also worked to strengthen their defensive positions in Boston, but General Burgoyne also suggested they use their ships and troops to antagonize the rebels in towns along the southern coast of New England.

Burning of the Guardhouse at Boston Neck and Boston Harbor Lighthouse

Small skirmishes between the Continental Army and British regulars continued throughout the summer.

On July 8, a small force from the Continental Army attacked the British guardhouse at Boston Neck. They routed the British and burned the guardhouse to the ground.

On July 21, an expedition led by Joseph Vose and Benjamin Tupper was sent by Washington to Brewster’s Island, where the lighthouse was located. They set fire to the wooden parts of the lighthouse but were chased off by the British. The damage to the lighthouse was not permanent, and the British were able to make repairs. A second raid on the lighthouse occurred on July 31, under cover of night. They took the British by surprise, overwhelmed them, and set fire to the lighthouse, this time rendering it useless to British ships in the harbor.

Washington grew impatient over the summer and looked for a way to attack the British in Boston. He held a council of war with his generals on September 11 and proposed an attack. His generals were against the idea, and the stalemate continued. A second council was called in October, with the same result.

Howe Replaces Gage — October 10

On October 10, William Howe replaced Gage as commander-in-chief of the British forces in North America. Gage returned to England the next day. With Howe in command, there was little change in the British strategy. He continued to strengthen existing defensive positions in Charlestown, on Bunker Hill, and at Boston Neck. He also started building new batteries on Beacon Hill and at Boston Common.

This illustration depicts General William Howe, who replaced Thomas Gage. Image Source: Wikipedia.

Franklin Meets with Washington — October 18

A little more than a week later, on October 18, a committee, sent by the Continental Congress, and led by Benjamin Franklin, met with Washington, his staff, and delegates from Massachusetts, Connecticut, Rhode Island, and New Hampshire. This meeting resulted in the reorganization of the Army, the promise of more troops, and a system for supplying clothing and supplies for the Army. When the committee returned to Philadelphia, the plan was approved by Congress.

Skirmish at Lechmere Point — November 9

On November 9, 1775, Howe launched a small offensive, sending an expedition to Lechmere Point to seize cattle. Colonel William Thompson attacked them with his Pennsylvania militia, with support from the Massachusetts militia under the command of Colonel Benjamin Woodbridge and Colonel John Patterson. The British were only able to secure 10 cattle before they were driven back.

The Knox Expedition

In an effort to break the stalemate in Boston, he sent Henry Knox to Fort Ticonderoga with orders to retrieve the heavy artillery that had been captured at the forts on Lake Champlain and transport it to Boston. Knox himself had presented the idea to Washington. The Knox Expedition left Boston on November 17 and reached Ticonderoga on December 5. Despite delays due to the winter weather the Expedition successfully moved 60 tons of cannon and other weapons to the camps of the Continental Army outside of Boston, covering approximately 300 miles.

On January 16, 1776, Washington called a council of war and proposed an attack on the British. Washington wanted to attack before more British reinforcements could arrive in the Spring. Less than a week later, the Knox Expedition arrived in Framingham, Massachusetts, east of Boston, on January 25. Knox wrote to Washington, informing him that he had 59 pieces of artillery with him, and all of it was ready to be turned over to the Continental Army. The weapons were moved to Cambridge on January 27. By late February, the artillery, including 35 cannons, had been moved from Cambridge to Roxbury.

Washington tried again on February 16 and 18 to convince his officers to mount an attack on the British. They still disagreed, because they felt that any attack would need to be preceded by artillery bombardment on British defenses, and the Army was short on manpower and gunpowder. Instead of planning an offensive, the council resolved to make preparations to take Dorchester Hill as soon as there was enough firepower. They believed this action would draw the British out of Boston, off of Noodle’s Island, and out into the open.

Fortification of Dorchester Heights

Finally, the Continental Army was ready to make a move. Washington planned to move the artillery to Dorchester Heights, but a distraction was needed.

The Continental Army launched a 3-day bombardment on the British on the morning of March 2, using some of the cannons that had been captured at Fort Ticonderoga and Crown Point. The artillery had been placed at Lechmere’s Point, Cobble Hill in Cambridge, and Lamb’s Dam in Roxbury. The artillery batteries in Cambridge also painted logs to make them look like cannons. This gave the British the impression the Continental Army had more firepower than it really did.

Siege of Boston, Fortification of Dorchester Heights, 1776
This painting by Louis S. Glanzman depicts the American position at Dorchester Heights. Image Source: National Park Service.

On March 3, troops under the command of General John Thomas quietly marched to Dorchester Heights, muffling the sound of their wagon wheels with straw. They moved the artillery from Ticonderoga, tools, and pre-fabricated fortifications to the top of the hill. By the next morning, they had built the fortifications and had their cannon pointed at the British ships in Boston Harbor.

The British planned an offensive, but two things prevented them from moving ahead. First, Washington learned of the plan and increased the number of troops on Dorchester Heights. Second, a snowstorm hit Boston on March 5.

British Evacuate Boston — May 17, 1776

On March 7, Howe decided to evacuate the British troops from Boston. 11,000 British troops were joined by nearly 1,000 Loyalists on the retreat. Although they blew up Castle William in Boston Harbor when they departed, they had agreed not to burn Boston during the retreat, as long as the Americans did not attack. The British contingent marched five miles south of Boston, to Nantucket Roads, where they stayed until March 17.

The British set sail for Halifax, Nova Scotia on March 17, now known as Evacuation Day in Boston.  That same day, Artemas Ward and 500 of his men entered Boston, ending the siege. The next day, General Washington visited Boston, and the main forces of the Continental Army moved into the city on March 20. The British had left 69 cannons behind that the Continental Army was able to salvage and make use of.

This illustration depicts Washington and American forces watching the British sail out of Boston Harbor on Evacuation Day. Image Source: New York Public Library Digital Collections.

Significance of the Siege of Boston

The Siege of Boston was an important event in the history of the United States because it showed how colonists in Massachusetts and other colonies in New England were not afraid to stand up to the military power of the British army. Once George Washington took command, he was able to keep the army in place and continue the siege long enough for Henry Knox to return from Ticonderoga. Eventually, the British left the city, and the colony of Massachusetts — and never returned — which made Massachusetts the first American state to completely break free from Britain.

Important American Revolution Events in Boston

Boston Massacre, Illustration, Chappel

March 5, 1770 — The Boston Massacre. On that night, British troops fired into a crowd and killed five colonists, including Crispus Attucks.

Boston Tea Party, Illustration, Currier

December 16, 1773The Boston Tea Party. The Sons of Liberty dumped more than 340 chests of tea into Boston Harbor to protest the Tea Act.

September 1, 1774 — Powder Alarm. After British troops removed military supplies from Cambridge, thousands of militiamen descended on Boston.

Important Facts About the Siege of Boston

Beginning of the Siege

  • After the Battle of Lexington and the Battle of Concord, British troops marched back to Boston.
  • Along the way, American militia forces shot at them, including at Parker’s Revenge and the Battle of Menotomy.
  • When the British reached Charlestown, the Americans stopped their pursuit because there were British ships in the harbor that could fire on them.
  • The Americans stayed out of range of the guns and set up camps at Cambridge and other areas around Boston.

American Militia Forces Organize

  • Rhode Island, New Hampshire, and Connecticut sent militia forces to help keep the British trapped in Boston.
  • The militia forces set up a siege line from Chelsea, North of Boston, to Roxbury, South of Boston
  • On April 23, the Massachusetts Provincial Congress voted in favor of calling more men to arms and putting the Massachusetts militia under the command of Artemas Ward.
  • Joseph Warren was named Major General of the Massachusetts militia.
  • The other colonies agreed to put their forces under the command of Ward in what was referred to as the Army of Occupation.

British Fortifications

Gage had fortifications built at:

  • Barton’s Point
  • Copp’s Hill
  • Fort Hill
  • Across the road to Roxbury
  • Beacon Hill

British Reinforcements

On May 25, the HMS Cerberus arrived with reinforcements and three Generals:

  1. John Burgoyne
  2. Henry Clinton
  3. William Howe

Congress Creates the Continental Army

  • On June 14, the Continent Congress reorganized the Army of Occupation into the Continental Army.
  • On June 15, George Washington was named Commander-in-Chief.

Battle of Bunker Hill

  • During the night of June 16, American forces built fortifications on Breed’s Hill.
  • On June 17, the British bombarded Charlestown and then launched an assault on American positions.
  • The British charged up the hill twice and were driven back.
  • However, the Americans ran out of ammunition, and when the British stormed the hill a third time they overran the Americans and forced them to run.
  • Joseph Warren was killed in the retreat.
  • Major John Pitcairn, who led the British infantry into Lexington on the morning of April 19, was killed during the battle. Legend has it that an African-American, Peter Salem, was responsible for the shot that killed Pitcairn.

Changes in Command

  • Washington arrived at Watertown, Massachusetts on July 2. The next day, he took command of the army at Cambridge the next day.
  • On October 10, William Howe replaced Gage as Commander-in-Chief of the British forces in North America.
  • Gage sailed to Britain on October 11.

Americans Force the British to Evacuate Boston

  • On January 25, Henry Knox and his men arrived with cannons and guns they had retrieved from Fort Ticonderoga.
  • In early March, the Americans placed the artillery around Boston and started bombarding British positions.
  • On March 3rd and 4th, the Americans placed cannons on Dorchester Heights, close enough to fire on the British fleet in the harbor.
  • Howe decided to evacuate Boston on March 7.
  • The British marched out of Boston and went five miles south, to Nantucket Roads.
  • The British stayed there until March 17, when they boarded their ships and sailed to Halifax, Nova Scotia.
  • March 17 is known as Evacuation Day in Boston.

Siege of Boston Timeline

This list shows the main battles and events that took place before and after the Siege of Boston, and how it fits into the chronological order of the Boston Campaign.

  • April 18–19, 1775 — Midnight Rides of Paul Revere, William Dawes, and Samuel Prescott
  • April 19, 1775 — Battle of Lexington
  • April 19, 1775 Battle of Concord
  • April 19, 1775 — Parker’s Revenge
  • April 19, 1775 — Battle of Menotomy
  • April 19, 1775 — Siege of Boston Started
  • April 23, 1775 — Artemas Ward was Placed in Command of the Massachusetts Militia Forces
  • May 10, 1775Capture of Fort Ticonderoga
  • May 10, 1775Second Continental Congress Started
  • May 25, 1775 — British Generals John Burgoyne, Henry Clinton, and William Howe arrived in Boston
  • May 27, 1775 — Battle of Chelsea Creek
  • June 12, 1775 — Thomas Gage Offered Pardon to All Rebels Except for Samuel Adams and John Hancock
  • June 14, 1775 — Continental Congress Organized the Army of Occupation into the Continental Army
  • June 15, 1775 — George Washington was Named Commander-in-Chief of the Continental Army
  • June 17, 1775Battle of Bunker Hill
  • July 3, 1775 — George Washington Took Command of the Continental Army
  • October 10, 1775 — William Howe Replaced Thomas Gage
  • November 9, 1775 — Skirmish at Lechmere Point
  • November 17, 1775 — Knox Expedition Left Boston
  • January 25, 1776 — Knox Expedition Arrived in Framingham
  • March 3, 1776 — American Occupation of Dorchester Heights
  • March 7, 1776 — Howe Decided to Evacuate Boston
  • March 17, 1776 — Evacuation Day

Siege of Boston Frequently Asked Questions

Who won the Siege of Boston?

The United Colonies won the Siege of Boston. On March 3, 1776, Continental Army forces placed cannons on Dorchester Heights. The position gave the Americans a tactical advantage and they could fire on the British ships in Boston Harbor. The British decided to evacuate Boston and left on March 17.

Was the Siege of Boston successful?

Yes, the Siege of Boston was successful — in more ways than one. First, American forces stood up to the British after Lexington and Concord. Second, many colonies sent militia to reinforce the Massachusetts Militia. Finally, Washington was able to keep the army together long enough to force the British evacuation.

When was Evacuation Day in 1776?

Evacuation Day in 1776 was on March 17, 1776. On that day, around 11,000 British troops and hundreds of Loyalists who lived in Boston left the city. They boarded the British ships that were in Boston Harbor and sailed to Halifax. However, the Americans did not know the destination

Siege of Boston APUSH, Review, Notes, Study Guide

Use the following links and videos to study the events of April 19, 1775, the Siege of Boston, and the American Revolutionary War for the AP US History Exam. Also, be sure to look at our Guide to the AP US History Exam.

Siege of Boston APUSH Definition

The Siege of Boston was a prolonged military blockade that began in April 1775 and lasted until March 1776 during the early stages of the American Revolutionary War. Colonial forces, primarily the Continental Army, surrounded British-occupied Boston, preventing the British from resupplying or reinforcing their troops. The siege culminated with the American capture of Dorchester Heights, which forced the British to evacuate Boston.

Siege of Boston Video for APUSH Notes

This video from the American Battlefield Trust provides a quick overview of the Siege of Boston.

Read About the Siege of Boston

The books on this list tell the story of the Siege of Boston, including the events that led to it, the battles and skirmishes that took place, and the outcome. These books — and others — were used as sources for this article. The links will take you to, and if you buy anything, American History Central may earn a small commission.

Citation Information

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  • Article Title Siege of Boston
  • Date April 19, 1775–March 17, 1776
  • Author
  • Keywords Siege of Boston, Boston Campaign, American Revolution, American Revolutionary War
  • Website Name American History Central
  • Access Date June 13, 2024
  • Publisher R.Squared Communications, LLC
  • Original Published Date
  • Date of Last Update April 22, 2024