Editing Roman calendar (section)

==Conversion to Julian or Gregorian dates==
The continuity of names from the Roman to the [[Gregorian calendar]] can lead to the mistaken belief that Roman dates correspond to Julian or Gregorian ones. In fact, the essentially complete [[list of Roman consuls]] allows general certainty of years back to [[expulsion of Tarquin|the establishment]] of the [[Roman Republic]] but the uncertainty as to the end of lunar dating and the irregularity of Roman intercalation means that dates which can be independently verified are invariably weeks to months outside of their "proper" place. Two astronomical events dated by [[Livy]] show the calendar four months out of alignment with the Julian date in 190{{nbsp}}BC and two months out of alignment in 168{{nbsp}}BC. Thus, "the year of the consulship of [[Publius Cornelius Scipio Africanus]] and [[Publius Licinius Crassus Dives (consul 205 BC)|Publius Licinius Crassus]]" (usually given as "205{{nbsp}}BC") actually began on March 15, 205{{nbsp}}BC, and ended on March 14, 204 BC, according to the Roman calendar but may have begun as early as November or December 206{{nbsp}}BC owing to its misalignment. Even following the establishment of the [[Julian calendar]], the leap years were not applied correctly by the Roman priests, meaning dates are a few days out of their "proper" place until a few decades into Augustus's reign.

Given the paucity of records regarding the state of the calendar and its intercalation, historians have reconstructed the correspondence of Roman dates to their Julian and Gregorian equivalents from disparate sources. There are detailed accounts of the decades leading up to the Julian reform, particularly the speeches and letters of [[Cicero]], which permit an established chronology back to about 58{{nbsp}}BC. The [[nundinal cycle]] and a few known synchronisms—e.g., a Roman date in terms of the [[Attic calendar]] and [[Olympiad]]—are used to generate contested chronologies back to the start of the [[First Punic War]] in 264{{nbsp}}BC. Beyond that, dates are roughly known based on clues such as the dates of [[harvest]]s and seasonal [[Roman festivals|religious festivals]].