There is no year zero in this scheme, so the year AD 1 immediately follows the year 1 BC.This dating system was devised in 525 by Dionysius Exiguus of Scythia Minor, but was not widely used until after 800.For example, the Islamic calendar begins not from the date of the Hijra, but rather weeks prior, on the first occurrence of the month of Muharram (corresponding to 16 July 622).that Dionysius' desire to replace Diocletian years with a calendar based on the incarnation of Christ was intended to prevent people from believing the imminent end of the world.
The abbreviation is also widely used after the number of a century or millennium, as in "fourth century AD" or "second millennium AD" (although conservative usage formerly rejected such expressions).
taken from the full original phrase "anno Domini nostri Jesu Christi", which translates to "in the year of our Lord Jesus Christ".
This calendar era is based on the traditionally reckoned year of the conception or birth of Jesus of Nazareth, with AD counting years from the start of this epoch, and BC denoting years before the start of the era.
The Anno Domini dating system was devised in 525 by Dionysius Exiguus to enumerate the years in his Easter table.
His system was to replace the Diocletian era that had been used in an old Easter table because he did not wish to continue the memory of a tyrant who persecuted Christians.