<P> With these various styles, the same day could, in some cases, be dated in 1099, 1100 or 1101 . </P> <P> The date of birth of Jesus of Nazareth is not stated in the gospels or in any secular text, but most scholars assume a date of birth between 6 BC and 4 BC . The historical evidence is too sketchy to allow a definitive dating, but the date is estimated through two different approaches - one by analyzing references to known historical events mentioned in the Nativity accounts in the Gospels of Luke and Matthew, and the second by working backwards from the estimation of the start of the ministry of Jesus . </P> <P> During the first six centuries of what would come to be known as the Christian era, European countries used various systems to count years . Systems in use included consular dating, imperial regnal year dating, and Creation dating . </P> <P> Although the last non-imperial consul, Basilius, was appointed in 541 by Emperor Justinian I, later emperors through Constans II (641--668) were appointed consuls on the first 1 January after their accession . All of these emperors, except Justinian, used imperial post-consular years for the years of their reign, along with their regnal years . Long unused, this practice was not formally abolished until Novell XCIV of the law code of Leo VI did so in 888 . </P>

When did we switch from bc to ad