Pre-AD 1

Pre-AD 1 is a rare year mentioned by Denis while creating the gregorian calendar. It's the year before AD 1, and the first year of the Anno Domini system, starting on Thursday, the 1st year of the 1st millennium, the 1st year of the 1st century, and the 1st year of the 0s decade.

Although the year Pre-AD 1 is extremely rear to historians, and not seen in either the Julian or Gregorian calendar, a sixth century monk who goes by the name of Denis, mentioned while creating the calendar that there was a year in between 1 BC and AD 1. It's unknown today, it is not the year 0 however, because 0 did not yet exist in the 6th century.

Pre-AD 1 is a the second most rarest year in history, along with its predecessor B.A.D (Before Anno Domini) which occurred after 1 BC and before Pre-AD 1.