BOSTON (AP) — Reenactors in 18th-century military coats and tricorn hats filled the pews of one of the nation's oldest Catholic Churches on Tuesday before firing muskets outside and marching through neighborhood streets, marking the 250th anniversary of the day British forces evacuated the city.

Men, horses and even cattle moved through South Boston’s hills in the morning wind as residents watched from stoops — some in pajamas and wrapped in blankets, appearing to have been awakened by the sound of drums and bagpipes.

Evacuation Day commemorates March 17, 1776, when British troops withdrew from Boston after months of siege by colonial forces. The breakthrough came when Gen. George Washington fortified Dorchester Heights with artillery hauled from Fort Ticonderoga by Col. Henry Knox, giving the Continental Army a strategic advantage over the harbor and forcing the British evacuation.

The evacuation marked the Continental Army’s first major victory of the Revolutionary War, ending an 11-month siege of Boston and securing the city for the American cause.

The ceremony Tuesday began at St. Augustine Chapel and Cemetery, where participants gathered for mass before forming a procession that moved through South Boston toward Dorchester Heights, the hill where colonial forces positioned artillery overlooking the harbor.

Ronald White of Milton, dressed in colonial attire, stood among a line of reenactors firing replica muskets in the church’s graveyard following the service and said the anniversary carries personal meaning.

A member of the New Hampshire Sons of the American Revolution, he traces his lineage to an ancestor who fought in the war. His eyes teared up Tuesday talking about how inspired he feels by the nation's founders.

“To think that 250 years ago Henry Knox made such a courageous stand, I get choked up thinking about it,” White said. “They really were going up against a force — it was kind of a suicidal idea to stand up against Great Britain. And we did it. Here we are remembering it.”