Dating practices through history
While the Gospel of Matthew states in chapter 2:1 that Jesus was born during the reign of Herod the Great, the Gospel of Luke states in chapter 2:1-2 that Jesus was born during the first census of the rule of Quirinius, governor of Syria.According to ancient sources, the date of this census is about 6 CE.In Mesopotamia, for example, one might date an event as "five years from the reign of King Shulgi" and, in Egypt, as "three years after the last Opet Festival of Ramesses who was the second of that name" or, otherwise, "In the 10th year of the reign of Ramesses who triumphed at Kadesh".This method of dating was continued by the Romans who counted their years according to three different systems in different eras: from the founding of Rome, by which consuls were in power, and by which emperors ruled at a given time.According to multiple ancient sources, Herod died in 4 BCE.If the Gospel of Matthew is historically accurate, this would mean that Jesus of Nazareth was born on or before 4 BCE—meaning Jesus was born 4 BC (4 years Before Christ)!If we add to these 4 years the fact that Herod the Great did not die immediately after the birth of Jesus, but, according to Matthew, ordered the death of all children two years of age and younger in an attempt to kill Jesus, we can add an additional two years to the birth of Jesus, making his birth approximately 6 BCE.
This goal had been decided upon by Constantine the Great at the Council of Nicea in 325 CE but had not yet been met.
The only problem with this dating system was that no one knew when Jesus of Nazareth was born.
Dionysius himself did not know when Jesus was born and his system makes no claims at dating that event definitively.
Julius Caesar (100-44 BCE) reformed the calendar and renamed the months during his reign (49-44 BCE).
This calendar remained in use, with periodic revisions, until 1582 CE when Pope Gregory XIII instituted the Gregorian Calendar still in use in the present day.