Of all the poetic forms created in the Middle Ages, the sestina is perhaps the silliest. It was almost certainly invented by the troubadour Arnot Daniel who had the good sense to only write one. It was later taken up by Petrarch, who really should have known better, and then imitated by those who admired Petrarch including at least one sixteenth century Englishman.
The sestina is created using six key words, and has six stanzas of six lines each with a concluding three line stanza at the end. The six key words appear at the end of one line each in the first stanza, and we shall call the order they occur in 1, 2, 3, 4, 5, 6. In the second stanza each line again is concluded with a key word, this time in order 6, 1, 5, 2, 4, 3. In the third stanza the words are shuffled the same way, so that the order is 3, 6, 4, 1, 2, 5. This continues until six stanzas have been completed. The six words are then used in the concluding three line stanza, with two key words per line.