One of the first systems used for measuring time in year epochs was the regnal system.
This system counted from the start reign of a leader and reset at the introduction of a new leader. It was widely used throughout the ancient Middle East and Mediterranean area and popularized by the Romans.
The Biblical author Luke used this system on at least two occasions: to describe the birth of Christ under the Governorship of Quirinius,1 and Jesus’ baptism being in the 15th year of the reign of Tiberius.2
This 15th year of Tiberius is critical in many computations, as this is the only solid evidence about the life of Christ that can be accurately measured.
This regnal system was used by the early Church historians, such as the third century Bishop, Eusebius of Caesarea, who claimed that Christ was born in the 42nd year of the reign of Caesar Augustus and the 28th year after the Battle of Actium.3 If one assumes that Eusebius’ dates are consistent with standard history, this would make Christ’s birth at 3 BC, or if we use a later Christian document called the Chronological Tables that used Eusebius’ account as the basis, it oddly changes the date to 1 BC/AD.
Clement of Alexandria also used the regnal system, “From Julius Caesar, therefore, to the death of Commodus, are two hundred and thirty-six years”.4 Commodus, the Roman emporer in the late 2nd century was his reference point for determining the birth of Christ. Based on his calculations, the death of Commodus was 192 AD, which is consistent with history.5 He then goes on to write, “From the birth of Christ, therefore, to the death of Commodus are, in all, a hundred and ninety-four years.”6 This would make Christ’s birth at 2 BC.
A later editor or Clement himself contradicted this date elsewhere. In another section he employed the reign of Augustus to date the birth of Christ stating “our Lord was born in the twenty-eighth year, when first the census was ordered to be taken in the reign of Augustus.”7 Clement does not indicate what he believed was the start date of Augustus’ reign. It was quite common for some at this time to date Augustus start by the historic war battle of Actium. This is commonly held to be at 31 BC. If Clement agreed with this date, then Christ’s birth would have been 3 BC. Perhaps the first date of 2 BC was common opinion during his era and 3 BC was the historic Church position.