The Siege of Boston: An Overview

From 1775-1776, Boston took center stage in the first major campaign of what would become the War for American Independence. The Siege of Boston lasted eleven months, following the battles at Lexington and Concord on April 19, 1775, until the British Evacuation of Boston on March 17, 1776.

During this siege, British forces—trapped in Boston—engaged colonial forces in a series of battles, skirmishes, and raids throughout greater Boston and Boston Harbor. Soldiers and civilians alike suffered and persisted under harsh siege conditions. Food and supplies were scarce, and the fear of an escalated conflict remained ever present.

Read on for a general timeline overview of the Siege of Boston and opportunities to learn more about both military happenings and civilian experiences.

Unrest in the Colony (1765 – 1775)

Following the Seven Years’ War, British Parliament began instituting taxes on the American colonies to pay down a growing national debt. Citizens of the Massachusetts Bay Colony responded with anger towards this increased oversight. For a decade, tensions grew in Boston. Specific flashpoints—including the 1765 Stamp Act, the 1770 Boston Massacre, and the 1773 Boston Tea Party—drove a growing number of colonists towards revolutionary ideas of freedom and self-determination from Britain.

A Rebellion Begins (April & May 1775)

By 1775, British authorities had closed Boston Harbor in response to the town’s continued political defiance. Patriot leaders started their own government in the countryside and began to prepare for war. The first armed conflict occurred on April 19, 1775, when British soldiers from Boston clashed with colonial militia at Lexington and Concord. British forces retreated into Boston, allowing New England colonial militia to establish defensive lines surrounding Boston. Loyalist and Patriot residents of Boston either hunkered down in this town under siege or fled to the countryside as refugees.

With the Siege of Boston now underway, both British and American leaders looked to the surrounding hills of Boston, as well as Boston Harbor and its islands, as key to victory. As a result, skirmishes on Grape Island and at Chelsea occurred in May.

The Battle of Bunker Hill (June 1775)

Knowing the strategic importance of controlling Boston’s hills, colonial leaders decided to take the high ground on Breed’s Hill. On the night of June 16, roughly 1,200 New England colonial militia fortified the hill. When British commanders saw the fortifications on the morning of June 17, they looked to respond with a crushing assault. That afternoon, 2,400 British soldiers landed on the Charlestown waterfront for a two-hour bloody battle, destroying the town in the process.

Washington Takes Command in Boston (July 1775)

On June 15, 1775, the Second Continental Congress assembled the Continental Army and appointed George Washington as commander-in-chief. Washington arrived in Cambridge to formally take command on July 3. He looked to solidify the colonial positions around greater Boston while addressing logistical challenges and turning undisciplined colonial militia into a unified fighting force.

Raids & Skirmishes in Boston Harbor (July – September 1775)

While British and colonial forces continued to fortify along the siege lines on the mainland, both sides looked to the harbor islands as contested territories. Throughout the summer, a series of raids and skirmishes occurred across several islands that had been identified as strategically significant.

The Siege in Winter (October 1775 – January 1776)

While cannon fire and small skirmishes continued throughout the fall and winter, both sides remained at a stalemate. During the harsh winter, civilians and British soldiers in Boston struggled with scarce resources and supplies. Colonial soldiers outside Boston faced similar harsh conditions. Meanwhile, Washington and his generals sought a plan to finally break the siege.

Dorchester Heights & Evacuation Day (February – March 1776)

Washington and his generals returned to Boston’s hills as the answer to end the siege. They chose to stealthily fortify Dorchester Heights, a strategically located elevation to the south of Boston. On the morning of March 5, 1776, British military woke up to fortifications on the heights and planned to respond with an attack. However, a major winter storm thwarted their attempt. With colonial forces towering over Boston and the main shipping routes of Boston Harbor, the British had no choice but to abandon the town.

On March 17, over 8,000 British troops and more than a thousand Loyalist refugees evacuated Boston and departed for Halifax, Nova Scotia. To the great relief of the Bostonians who remained, the Continental Army marched victoriously into Boston, ending the siege.

After the Siege (1776 – 1783)

Although the Siege of Boston had formally ended, several ships of the British naval fleet remained in the outer harbor. Naval skirmishes continued until colonial forces landed on some of the islands to fully expel the British from the harbor in June. Boston saw this final victory one month before the American colonies officially declared independence from Great Britain.

Boston and its harbor remained strategically vital to the cause of American independence. Over the next seven years, the French traveled through Boston, bringing aid and helping to fortifying the harbor against a future attack. Boston served as the largest open harbor in North America for allied merchant ships, American warships, and large French naval fleets through the end of the war.