I’ve posted a couple of times about the 2014 International Conference on the Science of Computus. It took place this last weekend and was every bit as strong and stimulating as I’d hoped. (I also tweeted highlights as it unfolded).

Computus is not mainstream, I think it’s fair to say. It is not ‘Kings! Power! Ritual!’.[1] You might not even know what it is. At its core, computus is the application of natural sciences, maths and theology to the problem of when Easter falls each year. Easter is supposed to be held on the first Sunday after the first full moon after the vernal equinox. Because lunar and solar years are awkward lengths relative to each other, it took a long time to work out exactly how they fit together. The work involved encouraged people to develop astronomy, algorithms, and even historical form, since people were considering the structures of time itself. Sometimes different groups of people adhered to different solutions, and then there were fights.

Most famously, different observances in Scotland and Kent nearly ruined the marriage of Iona-educated King Oswiu of Northumbria, because he and his Kentish wife did not observe the same fasts and festivals. Eventually Oswiu called a synod in Whitby in 664 and it was agreed that the ‘Roman’ observance would be followed thereafter, and adherents of the Ionan Easter were invited to leave the kingdom. Unfortunately there was more than one ‘Roman’ observance on offer, so there followed over fifty years of bickering and the composition of many treatises on the subject.

That story is famous from Bede’s Ecclesiastical History, III.25. But the striking thing from the perspective of modern scholarship is that we didn’t really start to understand it until the early 1980s. It was then that Dáibhí Ó Cróinín – our host in Galway – discovered the only known copy of that rejected Ionan Easter reckoning. The text was corrupt but he teamed up with computer scientist Dan Mac Carthy (also at the conference) to reconstruct the data. Only then did we know just how out of sync the Ionan and Roman reckonings were – sometimes by a whole month. Many technical details have only fully been understood with the discovery of other texts, such as the Irish Computus Einsidlensis found by Immo Warntjes (also at the conference) in Switzerland in 2005.

The Easter Table of St Willibrord (c. 703)
The Easter Table of St Willibrord (c. 703)

In fact, the great thing about modern computistical studies is that new texts are still being discovered which transform our knowledge of the subject. This year’s Galway conference alone had a number of great examples. You might already have read my paper on an Iro-Lombard treatise from 747. This fitted nicely with a paper by Jacopo Bisagni, in which he discussed a number of unstudied texts he had found in manuscripts from Brittany. Leofranc Holford-Strevens introduced a hitherto unknown Frankish text from 775 which played with the Byzantine chronological system. (Sadly both the author and the scribe seem to have been completely incompetent, to judge from the number of mistakes Leofranc found in it). Immo read out a paper by Alden Mosshammer about an Iberian treatise from the seventh century, re-edited in the ninth, but which has never been properly studied. It shows that Easter controversies were resolved in Spain just before they were about to explode in Ireland and England.

Christian Etheridge gave us a tour of Icelandic computistical texts. Because of sagas, it is fair to say that most scholars who work on Iceland do kingship, law and conversion. I didn’t even realise there were twelfth-century Icelandic computistical texts.[2] We were all surprised to hear just how in-step with wider European intellectual trends they were, notably with the inclusion of Arabic astronomical knowledge. There is so much still to be discovered.

Discovery is only the first step. There is a wealth of treatises from the eleventh and twelfth centuries, for instance, which have been known for a while but which have received little scholarly attention. This is because these texts need to be edited with commentaries to make them accessible. But progress is being made here too now. Alfred Lohr is editing or co-editing a number of them, and his excellent edition of the Computus of Gerland – one of the most successful and popular treatises on the subject – appeared late last year. Immo Warntjes discussed how he had been working for MGH on finishing Arno Borst’s 1990 edition of the computus of Herman the Lame, from Reichenau early in the eleventh century. And Philipp Nothaft was able to launch his new edition of all five Christian treatises on the Jewish calendar from the period. Suddenly working on this material is going to be a lot easier.

And then we’ve got to work out what it all means. Obviously, we try and build in theories and models as we go along. Still, not every text announces its significance without some hard work. Ivana Dobcheva discussed medieval star catalogues which often accompany computistical treatises. But these are often so sketchy, she argued, that they could be no more than primers for evening lessons outside with an expert. Sometimes they must have been deluxe items for learned aristocrats. Rob Gallagher’s example of the ‘Metrical Calendar of Hampson’ probably falls into the same category. Produced shortly after the reign of Alfred, and preserved best in Æthelstan’s Galba Psalter, the calendar probably best reflects the symbolic importance of time to a king, rather than anything more technical. (See, I said computus was relevant to ‘Kings! Power! Ritual!’).

There were many other great papers which made the conference even richer than I have summarised. You can still see the twitter feed to see what else was going on, as it will be at least a couple of years until Immo has the final essays off everyone, edits them, and gets it all into the Brepols press machine.

In the meantime, we can look forward to a Festschrift in honour of Dáibhí Ó Cróinín – a richly deserved honour for a scholar who has done so much to promote not only study of computus, but also scholarship on medieval Ireland. Here is the moment when Pádraic Moran, flanked by Immo, made the announcement:


[1] Except sometimes it is of course.

[2] Not until Christian told me he was going to work on them a year or so ago, anyway.