The poet dreams that his loved one had died in a foreign place among strangers. The peasants nail her coffin shut, raise a rude cross above her coffin, and plant cypress trees around the grave. They leave her to the "indifferent stars" until the finds her and writes her epitaph: "She was more beautiful than thy first love / But now lies under boards."
The poem is based on Maude Gonne's journey to France to recover from fatigue. She had a predisposition to tuberculosis, so Yeats was worried that she would die in France, among strangers. He sent her this poem while she was there.
Perhaps more than any other, the poem expresses a conventionally Romantic disposition in Yeats. The setting - a foreign land - the subject - lonely death - and the upshot - that the poet can play a role in immortalizing the death of a beauty - are common themes in Romantic poetry. For instance, Wordsworth's famous poem "She Walked in Beauty" touches upon the same themes.