12 BC 12 BC Year 12 BC was either a common year starting on Saturday, Sunday or Monday or a leap year starting on Sunday (link will display the full calendar) of the Julian calendar (the sources differ, see leap year error for further information) and a common year starting on Friday of the Proleptic Julian calendar. At the time, it was known as the Year of the Consulship of Messalla and Quirinius (or, less frequently, year 742 "Ab urbe condita"). The denomination 12 BC for this year has been used since the early medieval period, when the Anno Domini calendar era
Julian calendar ordinary years in the Roman Republican calendar, from January to December, were: Sacrobosco then thought that Julius Caesar added one day to every month except February, a total of 11 more days to regular months, giving the ordinary Julian year of 365 days. A single leap day could now be added to this extra short February: He then said Augustus changed this, by taking one day from February to add it to Sextilis, and then modifying the alternation of the following months, to: so that the length of "Augustus" (August) would not be shorter than (and therefore inferior to) the