One of the ways flashbacks are used in poetry is to recollect a major event or turning point in a character's life. This occurs in Robert Frost's, "The Road not Taken," in which an unknown narrator recounts a time in his life when he was faced with two separate roads, one that was well-traveled, and another which was less-traveled. The narrator ends the poem with, "I took the one less traveled by, and that has made all the difference." He is looking back on his decision from many years past, and though he does not tell the reader how things turned out, it is clear that this choice early in his life affected everything that happened after he made his decision.
Another use of flashback in poetry is to show a moment from the past that represents a time of joy that a character no longer feels. Poets may use flashback to contrast a character's melancholy circumstances in the present with a happy event from childhood. Robert Frost's 1920 poem "Birches," is an example of this kind of technique. In it, a character observes swaying birch trees then later says, "So was I once myself a swinger of birches. And so I dream of going back to be." He flashes back to his childhood, and then back in the present he says, "I'd like to get away from earth awhile, and then come back to it and begin over." The narrator remembers the freedom and joy he experienced as a child swinging on birch trees and longs to return to that moment.
Epic poems such as Homer's "The Odyssey" were among the first to use the flashback technique to reveal a character's backstory in a dramatic fashion. In the "Odyssey," Odysseus, the main character of the narrative poem is first introduced in despair, a prisoner on Calypso's island. The reader is unaware of the events that put Odysseus on the island, an explanation which comes only after he escapes to Scheria and recounts in flashback the events that led to his imprisonment. Homer uses flashback to dramatize the backstory in a way that's more urgent and compelling than simply telling the audience the events in chronological order.
Flashbacks in poems can also build suspense. In Henry Wadsworth Longfellow's 1860 poem "The Midnight Ride of Paul Revere, the first five stanzas create the suspense of the title before flashing back to the event that took place in 1775. The lines are: "Listen my children and you shall hear of the midnight ride of Paul Revere. On the eighteenth of April, in Seventy-five, hardly a man is now alive who remembers that famous day and year." The next line "He said to his friend, 'if the British march by land or sea from the town tonight'," which immediately transitions us into the flashback of the actual ride for the rest of the poem.