Our text (Purgatorio 33.37-45) is a familiar one:

Non sarà tutto tempo sanza reda
l'aguglia che lasciò le penne al carro,
per che divenne mostro e poscia preda;
ch'io veggio certamente, e però il narro,
a darne tempo già stelle propinque,
secure d'ogn' intoppo e d'ogne sbarro,
nel quale un cinquecento diece e cinque,
messo di Dio, anciderà la fuia
con quel gigante che con lei delinque.

This is not an attempt either to “solve” the enigma forte or to review the myriad questions it has sponsored; rather, it is an effort to suggest an overlooked source for Dante’s formulation of his second “world-historical prophecy,” one which may, nonetheless, lend support to those who argue for the imperial dimension of this text. Dante’s first such prophecy has caused at least as much perplexity as has this one. One potential model for his mysterious prophecy of the veltro (Inf. 1.101), found in the first book of the Aeneid (1.278-296), has been discussed only sparingly. There Jupiter foretells (in one of the Virgil’s most significant prophetic gestures) the founding of the empire for which it is Aeneas’s task to prepare the way: “Hic ego nec metas rerum nec tempora pono; / imperium sine fine dedi” (vv. 278-279). For the view that there is indeed a Virgilian (and imperial) source for Dante's prophecy in the adjacent prediction of Augustus’s conquest of Furor and subsequent Roman control of the world (Aen. 1.286-296), see R. Hollander, Allegory in Dante’s “Commedia” (Princeton, 1969), pp. 90-91. This view was anticipated in a discussion that has not received much (or any?) attention (and was overlooked by Hollander). The author of the so-called “Ottimo commento” (reflecting on verses 100-111 of Dante’s first canto [DDP]) has heard the resonance of that Virgilian passage, even if he has mislocated it in a later book of the Aeneid: “Qui [Dante] seguita le parole di Virgilio nel sesto, ove disse, che Roma avrebbe imperio sanza fine.” Whether or not we can be certain that Dante was thinking of the great prophecy in Aeneid 1 in Inferno 1, it seems clear, if it has not been previously observed, that he was doing so in Purgatorio 33.

Dante’s “cinquecento diece e cinque” is, whatever its further significance, a number (515) expressed in three constituent parts (500 + 10 + 5). In Virgil, in the very passage that precedes his prophecy of Roman hegemony, Jupiter describes the period of time separating Aeneas’s military action in Latium and the founding of Rome. In its immediate context within the poem, his promise of Roman glory (Aen. 1.257-277) is offered as reassurance to his daughter, Venus, anxious about the future of her son. In this, Virgil’s first “historicizing” gesture in the Aeneid, Jupiter tells Venus of the three distinct chronological zones containing the pre-history of the Romans: (1) Aeneas will wage his war of establishment, (2) Ascanius will move the seat of rule from Lavinium to Alba Longa, (3) Romulus will be born there and eventually lend the offspring of Trojan Aeneas his own identifying and localizing name. These three “moments” all have temporal signals embedded in them. The first (Aen. 1.265-266) will last three summers and winters, or three years in all (tertia dum Latio regnantem viderit aestas, / ternaque transierint Rutulis hiberna subactis); the second (1.269-270), Ascanius’s continuance of Aeneas’s project, will consume thirty years (triginta magnos volvendis mensuribus orbis / imperio explebit...); the third (1.272), the period between Ascanius’s establishment of the kingdom in Alba Longa and the advent of Romulus as its ruler, will require three hundred (ter centum totos regnabitur annos). Thus the 333-year period separating Aeneas’s landfall in Italy from the birth of Rome proper is expressed by Virgil, just as Dante expresses the number of the DXV, in several of its possible parts (3 + 30 + 300).

It is inconceivable that Dante did not know or did not pay close attention to this passage. In fact, he almost certainly refers to it (even if Tozer’s gloss on the passage seems to offer the only precise statement to this effect found among the commentators) at Paradiso VI.37-38, when he says that the eagle of empire “fece in Alba sua dimora / per trecento anni e oltre.” The number that eventuates from the Virgilian passage is surely a propitious one, from Dante’s point of view: 333 is as trinitarian and as nine-based as the poet of Beatrice could possibly desire (see Vita nuova 29.3). It thus intrinsically opposes that worst of numbers, 666 (of which it is a better half), the number of the beast in Revelation 13:18, which had traditionally been read as a prophecy of the advent of Nero as Antichrist, and which has long seemed to commentators to be the antithetic numerical model for Dante’s “five hundred ten and five.”

The reason for Dante’s choice of 515 as the number given by Beatrice to her promised ruler/savior has never been resolved to general satisfaction. It is possible, as Robert Davidsohn argued a century ago (“Il ‘Cinquecento diece e cinque’ del Purgatorio,” Bullettino della Società Dantesca Italiana 9 [1902]: 129-131), that Dante was thinking of the period of time between Charlemagne’s coronation (800) and the pending reunification of Europe under the aegis of an emperor in 1315; it is possible, as E. G. Parodi believed (Poesia e storia nella “Divina Commedia” [Naples, 1920], p. 467), on the authority of such prophetic texts as De semine scripturarum (1205), that Dante looked upon 1315 as propitious because of the prophesied recovery of the Holy Land in that year; it is also possible, as Pietro Mazzamuto (“Cinquecento diece e cinque,” ED 2 [1970], p. 14) has suggested, that Dante is thinking of the date 1315 as the beginning of the sixth epoch of Christ prophesied in various medieval religious texts. It does seem reasonable to believe that some such historicizing view may have shaped his choice of the number, i.e., that he intended it to serve as a measurement of time between two great world-events. If he did, Virgil’s numbers would have seemed to him auspicious. Dante’s Christian 515 would thus represent a latter-day version of Virgil’s 333, a number that counters so dramatically the bestial 666 of the Apocalypse, the number of the establishment of the divinely sanctioned Roman empire, not of the rule of Antichrist.

In Dante’s poem there is at least one other passage involving numbers that may benefit from similar attention. In Paradiso 6.1-6, reflecting further on the rulership of the Roman eagle, Dante has Justinian speak of the “cento e cent’ anni e più” that separated the transfer of the capital of the empire to the newly constructed city of Constantinople (A.D. 330) and the coronation of Justinian (in 527). As has long been understood, first, among the commentators, by Tozer, in his gloss to Par. 6.4-6 in 1901, concurring with the earlier notice of Paget Toynbee (“The Chronology of Paradiso, VI, 1-6, 37-39,” The Athenaeum 3693 [6 August 1898]: 193, cited in Bullettino della Società Dantesca Italiana 6 [1899]: 195), Dante’s stretching of the historical record (which in fact allows only 197 years, not more than two hundred) is almost certainly the result of his having trusted the data he found in Brunetto Latini’s Tresor (1.87.2-4), which, in the version that Dante used, seems mistakenly to have presented these two dates as being 333 and 539, respectively, thus accounting for Dante’s phrasing to express what for him figured as 206 years, not 197. The language of that phrasing (“one hundred plus one hundred and more”) may remind us of the additive construction of the phrase “five hundred ten and five,” with which we began. Something else about it is, however, potentially still more arresting: Dante apparently believed that the “eagle,” the empire that grew from the enterprise of Aeneas, had lasted exactly 333 years after the birth of Christ, in the fulness of time under Augustus, to its unspeakable departure from Europe, the result of well-meaning Constantine’s shameful dereliction. And thus the 333 years necessary, in Virgil’s calculation, for the founding of Rome, Aeneas to Romulus, were countered by, in Dante’s calculation, the 333 years from the empire’s greatest glory to its disgraceful abandonment of its rightful seat. The 333 that Dante apparently found at hand in Brunetto’s book would likely have seemed to him, in light of Virgil’s positive use of that number, to suggest a sum (333 + 333) equal to the number of the beast. The negative political implications of the resulting 666 (Aeneas to Romulus, Christ to Constantine), reflecting the Donation and its dire result, are not difficult to grasp. It is precisely as an answer to such a dilemma that the 515, the “heir” of the “eagle” (Purg. 33.37-39), will manifest himself in order to restore the glory of God’s chosen empire.