One of my favourite poems, it's a villanelle, which is "a lyrical poem
of nineteen lines. A villanelle is structured with five tercets, that is to
say a three-line stanza, and a quatrain, a stanza consisting of four lines,
at the end." Each tercet expresses a distinct sentiment and seems to stand
on its own, all tercets being nicely wrapped up in the final verse, the
quatrain. You don't get the full effect without the necessary pauses
between the tercets and the concluding quatrain.
Another villanelle worth checking out is William Empson's Missing Dates.
