Dante masterfully applies the tenets of medieval numerology which infuses both the structure of his realms and his characters with much more depth than a simple surface narrative would suggest. Two notable uses of number-symbols applied to the structure of the Comedy include Dante’s cross-canticle use of the number eleven and the patterns found at the center of the Comedy, Purgatorio XVII. In all of the Comedy, Dante only makes explicit mention of the number eleven once, in the tenth bolgia of the eighth circle of hell. The mention is in reference to its size: “…although it turns for eleven miles and is no less than half a mile across” (Inferno 30.85-86). Furthermore, in the previous bolgia, Dante gives us another indication as to geographic size: “…think, if you believe you could number them, that the valley turns for twenty-two miles” (Inferno, 29.7-9). By using a multiple of eleven, not only is Dante giving us clues to the size of each circle relative to one another, he is more importantly linking the structure itself to the root number eleven, a number filled with transgression. A handful of traditions trace the origin of transgression to the number eleven, two of which will be familiar with most readers. In pre-Christian times, God gave the Jewish people the Decalogue, ten core laws to govern behavior and morality in accordance with the desires of God. The number eleven signifies a “stepping past” the Decalogue—a transgression of its tenets. According to a different perspective, the number twelve represents the fullness of apostolic truth as it aligns with the number of the apostles chosen by Christ. Note that upon the transgression of Judas, only eleven apostles remained, and this state was quickly amended by selecting Matthias to succeed Judas. The Venerable Bede keenly summarizes: “For eleven, which goes beyond ten but does not reach twelve, that is, the apostolic number, signifies transgression of the Decalogue of the Law.” The clever reader of the Comedy will immediately notice another connection with the number eleven through cross-canticle readings of Inferno XI, Purgatorio XI, and Paradiso XI. Dante reserves the whole of Inferno XI for an exposition of the types and degrees of sin that are punished in hell, and orders them in relation to how greatly they offend God. Thus, the theme of Inferno XI is the concept of sin itself (not merely an exploration of a particular sin). Purgatorio XI again addresses sin, but a very particular type of sin, pride. In fact, pride is the ultimate sin, which informs and promotes all other types of sin. For the moment we turn our eyes from the desires of God to the desires of ourselves, sin starts to grow within us. Thus, where Inferno XI catalogued sin, Purgatorio XI teaches us of that sin from which all other sins flow. Finally, Dante beautifully closes his cross-canticle exploration of sin in Paradiso XI, where humility, the counter-virtue of pride is given treatment by Thomas Aquinas illuminating the person of St. Francis of Assisi. Thus, not only does Dante build the structure of hell on the number eleven, but he uses it throughout each realm to explain the nature of sin and how to conquer it.
One may suspect that the center of the Comedy, Purgatorio XVII, may hold special significance. In fact, this canto along with canto XVI and canto XVIII form a cross-canto exploration of two themes, love and free will. Beyond literally being the structural center of the Comedy, Dante uses symbolic numbers to call our attention to these themes as being the most important themes of the entire work. After analyzing the text, we find that these themes are framed by two particular terzine that make mention of free will. Within Marco Lombardi’s discourse, exactly twenty-five terzine prior to canto seventeen, he says, “If that were so, free choice would be destroyed in you, and it would not be justice to have joy for good and mourning for evil” (Purgatorio 16.70-72). Symmetrically, we see another mention of free will exactly twenty-five terzine after Canto seventeen as well. Virgil says, “This noble power Beatrice understands as free choice, and therefore see that you remember it, if she speaks to you about it” (Purgatorio 18.73-75). As medieval number theory would have us do, we must sum the digits of twenty-five (the number of terzine on either side on canto seventeen). That they sum to seven, the number of completeness, is significant. It is as if Dante is calling direct attention towards the terzine between these two points, and emphasizing that the themes of free will and love represent the culmination of his entire journey. Furthermore, the seven central cantos in the Purgatorio have a distinct pattern of line numbers: 151, 145, 145, 139, 145, 145, 151. Again, summing the digits of each line count we get: 7, 10, 10, 13, 10, 10, 7. On the ends, the number seven is seen framing these seven canti and representing their completeness. Inside the frames, on both sides, is the number ten, representative of perfection. The center canto’s sum, 13, seems not to have any particular significance outside of the fact that one hundred thirty-nine lines implies that the central terzina of that canto will be the number seventy, whose digits sum to seven, once again reflecting completeness. As Singleton notes, “the area of these 7 cantos holds the experience of a ‘conversion’…variously presented in explicit statement and in imagery…[concerning] the radical difference that there is between possessing earthly goods and possessing heavenly goods.” Singleton’s relatively recent discovery illustrates the depth to which Dante infused his Comedy with number-symbols. In doing so, it helps the reader—even 700 years later—discover layers of meaning that aren’t found on a surface reading.
Beyond structure, Dante also uses symbolic numbers to provide meaning to individuals, or groups of individuals. Upon arriving in Limbo, Dante is met by great men of the past—Homer, Horace, Ovid, Lucan—and is made “sixth among so much wisdom” (Inferno 4.101-102). Being one of his earliest experiences in hell, it’s odd that he has such a positive experience. For a man like Dante, this is one of the greatest honors he could achieve. We will see this juxtaposition of negative (being in hell) and positive (lauded by the poets) infuse the story with meaning throughout this canto. Shortly after meeting the poets, Dante comes upon “a noble castle, seven times encircled by high walls, defended all around by a lovely little stream” (Inferno 4.106-108).
The Poet makes explicit reference to “seven” walls, reminding us of the symbolic meaning of completeness. Noted Dante scholar, Charles Singleton, explains, “Probably the noble castle is best understood as the Castle of Fame, special dwelling of those whose ‘honored name’ has won them a privileged place in Limbo. In that case the seven circles of walls, each with its gate leading to the castle, may well represent the seven liberal arts, and perhaps also the seven virtues, moral and intellectual, so well known to the pagans.” This episode is odd in a sense that even though we’re early on in hell, we see a reference to “completeness.” If these men are complete, why are they in hell? To that end, we must explore what other mention Dante makes of these pagans. He tells us that “…people worthy to be honored possessed that place” (Inferno 4.71-72), but that “…they did not receive baptism, which is the gateway to the faith that you believe” (Inferno 4.35-36). In fact, we see Dante repeatedly referencing a “falling short” of these virtuous pagans. “I am Virgil, and for no other crime did I lose Heaven than for not having faith…not for doing, but for not doing have I lost the sight of the high Sun…there I dwell with the innocent little ones” (Inferno 7.7-8, 7.25-31, emphasis added). Guzzardo explains, “They have been given a privileged place in Limbo precisely because these great men embody all the human qualities necessary for salvation except for one shortcoming: they lack that faith of which Baptism later became the sign.” Therefore, if we recall the symbolic representation of the number eight, baptism and salvation, we can see a beautiful positioning of completeness, in the sense that they were virtuously complete, yet they were lacking one thing, faith in a Redeemer or the Sacrament of Baptism which represents that faith. The seven walls actually represent a lacking on the part of the virtuous pagans. They accomplished everything they could through their humanity, but still fell short in their faith, and lost their salvation.
 Victoria Kirkham, “Eleven is for Evil: Measured Trespass in Dante’s Commedia,” Allegorica: A Journal of Medieval and Renaissance Literature Vol. 10 (1989), 31-32.
 Kirkham, “Eleven is for Evil,” 28.
 Charles S. Singleton, “The Poet’s Number at the Center,” Modern Language Notes Vol. 80, no. 1 (1965), 1-10.
 Guzzardo, Numerological Studies, 42.
 Guzzardo, Numerological Studies, 47.
 Guzzardo, Numerological Studies, 53.