Ideas: A History of Thought and Invention, from Fire to Freud

by Peter Watson

The calendar in use at the time Exiguus made his calculations was based on the accession of the emperor Diocletian, which took place in 285. Thus, the year that we call 532 was for Dionysius the year 247. But Exiguus didn’t see why time should start with a pagan emperor and it was during his Easter calculations that the abbot conceived the idea to divide time according to the birth of Christ. And here there befell Exiguus an extraordinary numerological coincidence. Victorius of Aquitaine, as we have seen, had come up with a 532-year cycle. As Exiguus worked back, in the year we call 532, he found that a Victorian cycle had begun in the very year in which he believed that Christ had been born–what we now call 1 BC. In other words, the sun and the moon, at the time he was working, were in exactly the same relation as they had been when Jesus was born. This was too much of a coincidence and, in the words of the Venerable Bede, confirmed for Dennis that 1 BC was indeed the year ‘in which He deigned to become incarnate’. From then on, and thanks to Dennis, dates were given as Anni Domini, ‘years of the Lord’. However, it was not until the eighteenth century that it became customary to designate the preceding era ‘before Christ’.87

AD BC explanation