The Spanish era counted the years from 38 BC, probably the date of a new tax imposed by the Roman Republic on the subdued population of Iberia.
The date marked the establishment of Roman rule in Spain and was used in official documents in Portugal, Aragon, Valencia, and in Castile, into the 14th century.
The instant, date, or year from which time is marked is called the epoch of the era. 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).
Each year at the Akitu festival (celebrating the Mesopotamian new year), one of a small group of high officials (including the king in later periods) would be chosen by lot to serve as the limmu for the year, which meant that he would preside over the Akitu festival and the year would bear his name.
Sometimes one or both consuls might not be appointed until November or December of the previous year, and news of the appointment may not have reached parts of the Roman empire for several months into the current year; thus we find the occasional inscription where the year is defined as "after the consulate" of a pair of consuls.It was used in Gaul, in Egypt until the Islamic conquest, and in the Eastern Roman Empire until its conquest in 1453.The rule for computing the indiction from the AD year number, which he had just invented, was stated by Dionysius Exiguus: add 3 and divide by 15; the remainder is the indiction, with 0 understood to be the fifteenth indiction.Another system that is less commonly found than might be thought was the use of the regnal year of the Roman emperor.At first, Augustus indicated the year of his reign by counting how many times he had held the office of consul, and how many times the Roman Senate had granted him Tribunican powers, carefully observing the fiction that his powers came from these offices granted to him, rather than from his own person or the many legions under his control.
About AD 400, the Iberian historian Orosius used the AUC era.