I’ve blogged here a couple of times about ancient time-reckoning, once about consular formulae, and another time about indictions. Today, I was looking through the collection of sermons preached by Leo the Great, subject of my Ph.D. dissertation. Leo’s sermons were published by him as a collection and they were organised by which feast of the Christian year they were preached. Leo is a thematic, not expository, preacher. The collection begins with the commemoration of his accession to the Roman episcopate on 29 September 440, with sermons from 440, 441, 443, 444, and 445. It ends with the September fast, with sermons spanning 441-458, which is almost his whole career as bishop of Rome. They are organised in order of when they occur in the year.
What does this have to do with dating?
Well, the indiction cycle starts on 23 September. So Leo’s sermon collection takes you through a full liturgical year — starting with the indiction.
One would expect one of two other situations. Either Leo would begin with Advent, since that is currently when the western liturgical year begins, or he would begin with 1 January since that is when the Roman civic calendar begins with consuls taking office. After all, he dated his letters by consular year.
There may be something here. On the other hand, maybe he started the collection on 29 September since that is his accession date.