BC or AD

[Panapop]

What is the year called that followed 1BC?

[Chillum]

1ad

[Clanad]

There was no year 'zero'...

[Octavius]

The system of numbering years A.D. (for "Anno Domini") was instituted in about the year 527 A.D. by the Roman abbot Dionysius Exiguus, who reckoned that the Incarnation had occurred on March 25 in the year 754 a.u.c.(ab urbe condita, that is, "from the founding of the city (Rome)" ), with the birth of Jesus occurring nine months later. Thus the year 754 a.u.c. was designated by him as the year 1 A.D. It is generally thought that his estimate of the time of this event was off by a few years (and there is even uncertainty as to whether he identified 1 A.D. with 754 a.u.c. or 753 a.u.c.).

The question has been raised as to whether the first Christian millennium should be counted from 1 A.D. or from the year preceding it. According to Dionysius the Incarnation occurred on March 25th of the year preceding 1 A.D. (with the birth of Jesus occurring nine months later on December 25th), so it is reasonable to regard that year, rather than 1 A.D. as the first year of the Christian Era. In that case 1 A.D. is the second year, and 999 A.D. is the 1000th year, of the first Christian millennium, implying that 1999 A.D. is the final year of the second Christian millennium and 2000 A.D. the first year of the third.

Therefore, although Dionysus got his calc a bit muddled,  527 years afterwards, it was decided that it went 1BC or BCE (2 b pc) and then 1AD, but at the time, the year was probably called 753 o 754 after the founding of the city of Rome.