Today is the feast of Pope Leo the Great. Since his letters and the transmission are the major concern of my research, it is worth taking a moment to explain why he is Leo ‘the Great’ (and not just because he’s the first bishop of Rome named ‘Leo’).
There may be a temptation to weigh Leo’s greatness by our own scales — what is truly, timelessly, great about Leo? His rhetoric? His theology? His historical impact? His rulings in canon law? His preaching? A grand mixture of all of the above? While interesting, this would certainly not tell us why he is Leo ‘the Great’, since the only other pope universally called ‘the Great’ is Gregory I (590-604) — not everyone thinks of Nicholas I (858-867) in this regard, so I am unsure whether we have three ‘Great’ popes or only two.
Susan Wessel rightly rejected this approach in Leo the Great and the Spiritual Rebuilding of a Universal Rome. Unfortunately, she still answered the question in terms of what Leo’s intrinsic greatness may have been — only situating this greatness as people in his own era would have perceived it. The argument still has to do with seeking a unified answer in his corpus of writings and actions.
Neither of these approaches actually tells us why Leo is ‘the Great’.
Leo is one of the first — if not the first — articulate theologians of papal primacy. This is not why he is ‘the Great’.
Leo wrote more letters destined to be sources for canon law in the succeeding generations than any predecessor. This is not why he is ‘the Great’.
Leo wrote more surviving letters than any bishop of Rome before Gregory the Great. This is not why he is ‘the Great’.
Leo helped dissuade Attila the Hun from passing down into central Italy. This is not why he is ‘the Great’.
Leo left behind the first surviving corpus of sermons preached by a bishop of Rome. This is not why he is ‘the Great’.
Leo was the first bishop of Rome buried at St Peter’s. This is not why he is ‘the Great’.
Leo was very heavily involved in the geo-ecclesiology of his day, East and West, and he he helped organise the Council of Chalcedon in 451. This, too, is not why he is ‘the Great’.
Chalcedon gets us close, though.
Pope Leo I is called Leo Magnus, Leo the Great, because of his two-nature Christology as outlined in his letter to Flavian of Constantinople of 448 (the ‘Tome’, epistle 28 in the 1753 edition of the Ballerini, repr. Patrologia Latina vol. 54). In 451, Leo succeeded in having this Christology enshrined as the official dogma of the imperial church at the Council of Chalcedon, of which he was a chief player (although the Emperor Marcian was even more so), and he did his best after Marcian’s death, from 457 to his own in 461, to see that it was approved throughout the Empire and that various bishoprics were filled with Chalcedonian bishops.
He expounded it more carefully and more fully in his 124th letter to the monks of Palestine, which he re-used in his 165th letter to the Emperor Leo. This Christology was essentially the traditional Christology of the Latin West, with roots in Augustine of Hippo (who died in 430) and Hilary of Poitiers (who died in 368), and people had schisms over it in the decades after Leo died.
A lot could be said about what Leo’s contribution to theology was and how that contribution was interpreted and received by the imperial church in the century to come — and what would be said would be interesting, and it would highlight why those who loved Leo loved him greatly.
And this is why Leo is ‘the Great’ — theology.
(And how do I know this? Our earliest references to him as magnus, as cited in a 1911 article of C H Turner, are in relation to his status as a theologian of the person of Christ.)