After Lexington and Concord, New England militia surrounded British-held Boston and began constructing a broad ring of earthworks. When George Washington assumed command in July 1775, he inherited uneven fortifications, short enlistments, and severe shortages of powder and equipment. Strengthening the approaches to Cambridge was essential because the town contained headquarters, barracks, supply activity, and roads connecting the northern and western portions of the siege line.

Fort Washington was constructed in November 1775 on rising ground near the Charles River. The earthwork helped protect Cambridge and observe approaches associated with the river and nearby roads. Its name was applied later; during the siege it formed part of an integrated defensive landscape rather than operating as an isolated masonry fortress. Soldiers built embankments, ditches, platforms, and related works from soil and timber, using labor as a substitute for scarce heavy weapons.

The position supported the long containment of Boston while Washington tried to create a Continental Army from separate colonial forces. Daily service involved guard duty, fatigue labor, drills, patrols, and maintenance more often than direct combat. British troops remained protected by the harbor and Royal Navy, but American lines limited movement by land. The fort’s value lay in reducing the risk of surprise and allowing scarce troops and artillery to cover important ground.

The strategic balance changed when Henry Knox delivered heavy cannon from Fort Ticonderoga. In March 1776, American troops fortified Dorchester Heights and placed guns where they threatened the British fleet and city. General William Howe chose evacuation rather than a costly assault. On March 17, the garrison and many Loyalist civilians sailed for Halifax, ending the eleven-month siege and freeing Washington’s army to move toward New York.

Fort Washington is significant because surviving earthworks from the Siege of Boston are rare. Later restoration and commemoration shaped its present appearance, so it should not be viewed as wholly untouched since 1775. Even so, the site preserves the scale and logic of field fortification more directly than a roadside marker alone. It represents the sustained labor, vigilance, and organization that held the siege line before the dramatic occupation of Dorchester Heights forced the final British decision.

The Cambridge marker should not be confused with Fort Washington on the Hudson or the later Maryland fort of the same name. Revolutionary place names were repeatedly reused to honor the commander in chief, and modern databases can blur those distinct sites. Identifying the local topography and date keeps this position within the siege of Boston and prevents unrelated military histories from being merged.