); the latter means “in the year of the lord,” often translated as “in the year of our lord.” (It was thought when the AD dating system was created that its year 1 was the year Jesus of Nazareth was born.) was the first of these to appear.
Prior to the 6th century AD, many Christians who didn’t use an Anno Mundi (in the year of the world) type system relied on Roman dating, either marking dates from the year legend had it that Romulus and Remus founded Rome (753 BC) or by relying on the date system established under the Roman emperor Diocletian (244-311), based on the accession of Diocletian.
Previous to this, he had purportedly only advocated banning Christians from such things as the military and ruling body in hopes that would appease the gods.
Afterward, he switched to an escalating policy of persecution to try to get Christians to worship the Roman gods.
This began simply via seizing Christian’s property, destroying their homes, burning all Christian texts, etc.
When this sort of thing was ineffective, they progressed to arresting and torturing Christians, starting with the leaders.
When that didn’t work, Christians began to be killed in various brutal ways including occasionally being torn apart by animals for the amusement of the masses (Damnatio ad bestias).
This method of convincing people to worship the Roman gods ended up being an amazing failure and the persecution appears to have only continued after AD 305 in the Eastern half of the empire under Galerius and Maximinus.Finally, in April of AD 311, by imperial decree, the Great persecution was put to an end even in the East.A few years later, Constantine the Great (reigning from AD 306 to 337) publicly declared himself a Christian and Christianity began to transition into the dominate religion in the Roman Empire.In any event, Easter was/is the most important holy day of the Christian tradition, and it was decided at the First Council of Nicaea (AD 325) that it should occur each year on the Sunday following the first full moon after the spring equinox.In order to forecast when exactly the holiday fell each year, Easter tables were created.In AD 525, the monk Dionysius Exiguus of Scythia Minor was working on his table to determine when Easter fell when he decided to eliminate reference to Diocletian by listing his table’s first year as Anno Domini 532, explicitly stating this was referring to the year directly following the last year of the old Diocletian-based table, Anno Diocletiani 247.