The poem is titled "The Concord Hymn", and it was written for the dedication of the Concord Monument in 1837, commemorating the first major battle of the Revolutionary War.
The poem's famous opening lines, "By the rude bridge that arched the flood, / Their flag to April's breeze unfurled", refer directly to the events of April 19, 1775, when the first shots of the war were fired at the North Bridge in Concord.