Poets choose to compose rhyming verses for a variety of reasons, but few would ever consider rhyme as an instrument of survival. Rhyming couplets are easier to memorise than most other types of verse, but to think of rhyme as something meant to preserve the integrity of a poem is not quite common. And yet, this is what Dante thought when he invented one of the most complex rhyming patterns and allied it to an equally complex poetic structure in his Divine Comedy.
The epic poem was written in terza rima, a three-line rhyme scheme which carries the rhyme from one stanza to another like an unbroken chain. The pattern ABA BCB CDC DED EFE etc creates a bewitching effect, but also ensures that no line may be removed without destabilising the entire canto. This tripartite technique is wholly original, and it matches Dante’s other numerological concerns, the 3 of the Trinity, 100 cantos divided by three (34 for Inferno, and 33 for Purgatorio and Paradiso, each), plus internal correspondences and parallel cantos distributed across the poem.
Before the invention of print, texts were copied by hand, and errors of transcription were often made, involuntary alterations as well as omissions. It was a recognised issue built into the very fabric of the scribal culture which mobilised a great deal of effort, including the emergence of correctors which verified and emended the texts before they were published. It is the bread and butter of philologists, but a sad reality for the many ancient and medieval scribes.
Dante’s decision to create such an interlocking rhyming scheme for his poem minimised the corruptive effect of manual reproduction. The poema sacro (sacred poem, Paradiso 25) which he designed required an anti-oxydizing coating to ensure its integrity and survival. The omission of verses in the process of transcription was something, the scholars assure us, that Dante would not have conceded. So the terza rima created the last kind of textual protection for the 150 years or so before Gutenberg made things a lot easier for everybody.
Dante’s idea was very successful. Out of the surviving hundreds of manuscripts of the Comedy, none omits any verses at all. The chain held, the legno (the ship of Dante’s poem, Paradiso 2) was indeed watertight.