Anno Domini: the Origins of the Christian Era (review)

The dating system we use every day, based on 'the Year of the Lord' (Anno Domini), was, of course, invented in the medieval Christian West. In AD 525, to be precise, Dionysius Exiguus – a Scythian monk living in Rome – drew up a table of the dates of Easter Sunday covering a cycle of nineteen years. There was nothing particularly unique about this, nor about his giving various related numerical phenomena for the same period, including epacts, indictions, concurrents, and the age of the moon at Easter. What was unique, however, was that Dionysius identified each year in terms of the 'anni domini nostri iesu christi' (beginning with 532 AD). This was an important innovation; the earlier tables on which his table was based had used the year since the accession of the Emperor Diocletian to number each year instead. The Dionysian numbering of the years took a long time to spread across Western Europe and to replace numbering by the regnal years of Emperors, kings and other rulers. It was given an important boost by its use in the work of Bede in the early eighth century, and was then spread into the Frankish kingdoms by Anglo-Saxon missionaries.

Georges Declercq has produced a comprehensive study of the origins and early development of the Dionysian reckoning. He begins with a discussion of the scriptural evidence for dating the life and death of Christ, and the subsequent patristic tradition on these subjects. The later emergence of specifically Christian schemes for reckoning time is also covered, with particular emphasis on the practice of calculating the eras and years since creation, popularized by writers like Eusebius and Jerome. Declercq looks at the great controversies of the fourth and fifth centuries between the Roman and Alexandrian churches over the most appropriate basis for calculating the date of Easter Sunday. He shows how the work of Dionysius developed out of this continuing controversy.

There has been considerable scholarly discussion in the past of the motives and aims which lay behind the work of Dionysius. Declercq advances the hypothesis that Dionysius was not interested in an accurate historical calculation of the birth and death dates of Christ. He agrees with more recent scholars in rejecting the so-called 'computistical explanation' for the Dionysian system – the suggestion that Dionysius was trying to use the 532-year Easter cycle (the fact that the dates of Easter Sunday return to the same pattern after 532 years) to work back to a calculation of the historical dates of Christ's birth and death. Instead, says Declercq, he was motivated by a desire to promote the Alexandrian method of reckoning Easter, and was part of a much broader – and ultimately successful – movement to convert the Roman church to this method of reckoning. While the use of Anno Domini was a convenient way of numbering the individual years in an Easter table, it was not originally intended to be a numbering system for wider use.

Declercq's account of the intricacies of early Christian systems for reckoning time, and of the closely related controversies over the dates for Easter, is careful and painstaking. He manages to explain these complex and often abstruse techniques for calculation in a succinct and clear way. His book is an excellent guide to a subject which could all too easily become impossibly labyrinthine.