A poem that counts
Dante Alighieri wrote the Divine Comedy in Italian in the early fourteenth century, and he died in 1321. The poem describes a journey through Hell, Purgatory and Paradise, and its shape is unusually regular. Many of the numbers involved are plain facts about the text. What they mean is a matter of interpretation, and some readings are better supported than others.
Three parts, one hundred cantos
The poem has three books, called canticles: Inferno, Purgatorio and Paradiso. Inferno has 34 cantos, and the other two have 33 each, for a total of 100. The extra canto in Inferno is commonly read as an introduction to the whole poem, which leaves 33 cantos in each part. Thirty-three is a number that many readers link with the traditional length of the earthly life of Christ in years, although Dante does not say this outright.
One hundred is ten times ten, and some readers connect it with the old association of ten and completion found in several traditions. Whether Dante had that in mind is uncertain, but most scholars accept that the total of 100 was deliberate.
Terza rima
Dante invented the verse form called terza rima, in which lines are grouped in threes and the rhyme links each group to the next, in the pattern aba, bcb, cdc. The result is a chain in which each stanza leads into the following one. Each canticle ends with the same word, stelle, meaning “stars”.
The threefold form is often connected to Christian belief in a three-personed God, the subject of the Trinity doctrine. This association is widely accepted by readers, though it is an interpretation of why Dante chose the form. Three also shows up at the level of story: the poem opens with three beasts, three women in heaven send help to Dante, and Lucifer at the bottom of Hell has three faces. The wider habit of arranging material in threes, familiar from the rule of three in speech and storytelling, was available to him as well.
Nine and the shape of the afterlife
Hell is divided into nine circles, descending from the first, where virtuous non-Christians remain, through those of the lustful, gluttonous, hoarders and wasters, the wrathful, heretics and violent, to the fraudulent and finally the treacherous. Purgatory is a mountain with seven terraces, with a foothill region below and the earthly paradise at the summit, and its terraces follow the order of the seven deadly sins as medieval teaching presented them. Paradise has nine heavenly spheres, taken from the cosmology of his time, with the Empyrean beyond them.
So both Hell and Paradise have nine divisions. Some commentators also find a nine-part pattern in Purgatory by counting its foothill and summit along with the terraces, though how the mountain should be counted is debated.
The geography is not arbitrary. The medieval picture of the cosmos placed the earth at the centre, with the Moon, Mercury, Venus, the Sun, Mars, Jupiter and Saturn in turn, then the fixed stars and a ninth, outermost moving sphere, so nine was already a number in the astronomy Dante inherited.
Beatrice and nine
The clearest statement of Dante’s interest in the number comes from his earlier book, the Vita Nuova, which tells of his love for Beatrice. He says he first saw her when both were about nine years old, and he returns to the number several times in connection with her. He also offers a reason: nine is the square of three, and so Beatrice is like a miracle whose root is the Trinity.
This is Dante’s own explanation, and it comes from a poet describing a personal devotion, not a fact about numbers. It shows that he took numbers as part of the language of meaning and that he was willing to reason this way in public.
Other counts
Some other figures are less clear. The Comedy has about 14,000 lines, to be exact 14,233 by the usual count, with the three canticles of slightly different length: 4,720, 4,755 and 4,758 lines. Those numbers are known, but there is no consensus on whether the small differences were intended. Scholars have also proposed more intricate patterns in the placement of key words or episodes, and these are debated.
How to read the numbers
The sensible position is a middle one. The structure in threes, the nine divisions and the total of 100 cantos are so regular that most scholars accept a deliberate plan. The deeper claims, such as detailed numerical codes in particular lines, rest on less secure ground and are better treated as hypotheses.
The numbers also fit the habits of his age. Medieval writers, from the early church onward, often expected order in a work to reflect order in the world, a belief traced in Augustine on number. Dante can be read as an extension of that outlook into poetry. For him the numbers were part of how a poem about divine order could be built, and not a means of predicting anything.