A bold proposal

Chronicles past and present have derived much of their allure from the threefold promise of clarity, objectivity and reliability inherent in their structural format, which treats the chronological sequence of events as the very bedrock of history. The psychological benefits of this format are easily compromised, however, where chronicles are found to disagree with each other, or where the year counts used in different sources seem to resist synchronisation. Attempts to overcome these pitfalls by employing the tools of technical chronology have a long history that reaches back to antiquity. In the early decades of the twelfth century, the scribes at Worcester priory had the opportunity to contemplate a particularly far-reaching attempt in this direction as they laboured to augment and continue the famous Chronicon (or Chronica) by Marianus Scotus (1028–82/87), an Irish monk who had reviewed and revised the history of the world while living in voluntary enclosure in a cell in Mainz.

At the core of Marianus's Chronicon was the careful elaboration and defence of two interlocking chronological arguments. The first of these concerned the number of years between the creation of the world and the incarnation of Christ, which according to Marianus was 230 years higher than the 3952 years that Bede had counted on the basis of the Hebraica veritas of the Old Testament. The other argument entailed a substantial correction to the accepted number of years between the incarnation and the present, as based on the standard era ab incarnatione introduced by Dionysius Exiguus in the sixth century. According to Marianus, this interval had to be increased by no fewer than twenty-two years, as Christ's incarnation and birth really fell in the year we know as 22 BC. The technical foundation for both these proposed changes was supplied by the medieval computus and its 532-year Easter cycle, which resulted from combining two shorter calendrical cycles of nineteen and twenty-eight years. The nineteen-year ‘lunar’ cycle governed the recurring correlations between a given date in the Julian calendar and the concomitant age of the moon. The twenty-eight-year ‘solar’ cycle did the same for Julian dates and days of the week, while also predicting each year's position within the Julian pattern of leap years.