Sestina

The sestina is a poetic form invented by the twelfth-century troubadour Arnaud Daniel. It is composed of six stanzas of six lines each, followed by a three-line envoi. Each stanza must use the same six words to end each of its six lines. The ordering of these end-words within a stanza changes according to a fixed pattern. The final three lines must also employ these six words, usually two per line.

The ordering pattern is as follows:
The first line of a stanza uses the same end-word as the last (sixth) line of the previous stanza.
The second line uses the same end-word as the first line of the previous stanza.
The third line uses the same end-word as the fifth line of the previous stanza.
The fourth line uses the same end-word as the second line of the previous stanza.
The fifth line uses the same end-word as the fourth line of the previous stanza.
The sixth line uses the same end-word as the third line of the previous stanza.

Modern sestinas often use iambic pentameter and occasionally leave off the envoi.

References

The Ode Less Travelled, Stephen Fry, Hutchinson (2005), ISBN 0 09 179661 X
The Making of a Poem, Mark Strand and Eavan Boland, Norton (2001), ISBN 0-393-32178-9