Unfortunately, it was difficult in the sixth century AD for the originator of that system, Dionysius Exiguus, to determine the exact year when Christ was born.
The things he had to go on were the brief clues in the Gospels that relate Jesus’ birth or later age to events in Roman history, and the official Roman records of those events, neither of which were very precise.
As a result, his determination of the birth year of Christ was apparently off by about 4 years, but the error was not realized until centuries after the system had come into general use, leading to the strange circumstance that Christ was actually born in approximately 4 BC.
The months bore the names Martius, Aprilis, Maius, Juniius, Quintilis, Sextilis, September, October, November, and December—the last six names correspond to the Latin words for the numbers 5 through 10.In 452 BC, February was moved between January and March.By the 1st century BC, the Roman calendar had become hopelessly confused.Watching the countdown calendar to the publication day of INCEPTIO on 1 March reminded that the first of the month in the Roman system – the Kalends – ended up as our word for measuring the whole thing.In my Roma Nova thrillers, I use the standard Western system the world has agreed to use, but how did the traditional Roman system work? According to legend, Romulus, the founder of Rome, instituted the calendar in about 738 BC.The year, based on cycles and phases of the moon, totaled 355 days, about 10¼ days shorter than the solar year.