Annua Republikom

The Annua Republikom (Middle Alderaanian for "Years of the Republic") or Annos Respublicum (Old Coruscanti) was a calendar system used on certain Republic worlds prior to 10,000 BBY and was based on the year 25,053 BBY, which in folk legend was the year the Galactic Republic was founded between Coruscant, Alderaan, Corellia, Duros, and their colonies. This calendar was used concurrently with the Anno Liber ("Free Year") calendar, whose base year was set in around 27,500 BBY, which was around the time that Human slave colonies began overthrowing their Rakata overlords and established the first Human kingdoms and republics across the Core Worlds.

It was based on a twelve-month-long year, with each month numbering thirty or thirty-one days with the exception of the second month, which lasted twenty-nine days; each standard day was twenty-four hours, with each hour comprising sixty minutes, and each minute comprising sixty seconds. The Galactic Standard Calendar was modeled identically to this ancient calendar and both were based on Coruscant's orbital/rotational cycle.

History
It is unknown when this calendar was first used, with historians speculating that it was implemented on the very day of the Republic's conception, though the first records of the calendar discovered by modern archaeologists did not date back further than c. 10000 BBY. In around 5000 BBY, both the Annos Republicum and Anno Liber calendars were largely replaced with the Anno Corusantum (Old Coruscanti for "Year of Coruscant"), which retained the same measurements of time, though replaced its base year of 25,053 BBY/27,500 BBY with 5000 BBY, celebrating the end of the Great Hyperspace War. These three calendars would remain in use in Republic space as the primary calendar systems until the Ruusan Reformation of 1000 BBY, which established the Before-Ruusan/Post-Ruusan calendar system, which resulted in its three predecessors becoming completely phased out. Some worlds like Chandrila and Anaxes, however, still used the Annos Republicum calendar for traditional purposes well into the modern era.