A post in an online forum has drawn my attention to the letters of Pope Leo I (d.461). He is probably best known for persuading Attila the Hun to leave the defenceless city of Rome alone. Among patristicians, he is remembered for his Tome to Flavian, a letter sent to the Council of Chalcedon in 451 on the monophysite question, which was approved by the council and so committed the Roman see to supporting the decisions of that highly divisive council.
A collection of 173 letters, 30 of them by other people, is found in the Patrologia Latina volume 54. Among these is letter 133, which is not by Leo but addressed to him.
At that period the date of Easter was determined by a letter sent out by the patriarch of Alexandria. In 455, Leo wrote, querying the date given as being wrongly calculated. The patriarch was one Proterius. The emperor Marcian had appointed him, and he was deeply unpopular among the Alexandrian monophysites. After the death of Marcian in January 457, without bothering about Proterius they consecrated Timothy Aelurus (Timothy the Weasel) as patriarch, and on 28 March 457, during the celebrations of Maundy Thursday, Proterius was attacked and brutally lynched.
Proterius wrote back, commenting that possibly Leo had a bad copy or that a copyist had made a mistake. He also sent a copy of his letter in Greek, to make sure that no mistranslations got in the way. He justified the dating, pointing out that Easter was being celebrated a week late to avoid coinciding with the Jewish passover on 14 Nisan, which in 455 fell on a Sunday.
The online text of the PL is columns 1084-1094, although there are formidable notes so it’s probably about 7 columns of “normal” text. It’s long enough to be divided into chapters. I suppose a translation would not be that expensive, although I can think of no special reason to translate it.
Few of the letters of Leo have ever been translated into English. A selection by Edmund Hunt appeared in 1957 in the Fathers of the Church vol. 38. (I was going to link to a preview of this, which I saw at lunchtime today, but annoyingly I can’t find it on Google Books now!).
All the sermons of Leo seem to have been translated into German in the old BKV series, in the 2nd edition (vols. 54-55), here. According to Quasten, the letters were translated by Severin Wenzlowsky in 1869 in the first BKV series. The way in which the second edition left out material from the first — it applies to material by Tertullian also — has always baffled me. But I can find no trace online of any such volume. Wenzlowsky edited Der briefe der Papste in 1878 in this series, so it may be that Quasten was confused. These are all in a horrible Gothic font anyway.
I can find no information about French translations. René Dolle in the Sources Chretiennes series translated his sermons, in 4 volumes (22, 49, 74, 200) from 1947-73. But an earlier translation was made by a certain Pere Quesnel in 1698, and another by Nicholas Fontaine in 1701.
So … nothing, really. It is remarkable, tho, that the letters of so important a figure remain inaccessible!