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
365-day calendar length of 365 days with no rule for leap days, despite potential leap year rules being acknowledged by the 9th century at the latest. In particular, of the versions still in use today the Qadimi version does not have any form of leap rule; the Shahanshahi version had one leap month added in the 12th century but no leap years since, while the Fasli version (introduced in the 20th century) adds one day every four years. 365-day calendar A 365-day calendar consists of exactly 365 days per year (no leap days), and is primarily used in computer models and as