The use of consular dating ended in AD 541 when the emperor Justinian I discontinued appointing consuls.
In antiquity, regnal years were counted from the accession of a monarch.
This makes the Chronology of the ancient Near East very difficult to reconstruct, based on disparate and scattered king lists, such as the Sumerian King List and the Babylonian Canon of Kings.
Soon afterwards, imperial regnal dating was adopted in its place.
Another method of dating, rarely used, was anno urbis conditae (Latin: "in the year of the founded city" (abbreviated AUC), where "city" meant Rome).
It was rarely used in the Roman calendar and in the early Julian calendar – naming the two consuls that held office in a particular year was dominant.
AD 2018 is thus approximately the same as AUC 2771 (2018 753).
His successors followed his practice until the memory of the Roman Republic faded (about AD 200), when they began to use their regnal year openly.
Some regions of the Roman Empire dated their calendars from the date of Roman conquest, or the establishment of Roman rule.
The system was introduced by Marcus Terentius Varro in the 1st century BC.
The first day of its year was Founder's Day (April 21), although most modern historians assume that it coincides with the modern historical year (January 1 to December 31).
The instant, date, or year from which time is marked is called the epoch of the era.