History of calendars
Roman calendar and Julian calendar
Roman dates were calculated "from the founding of the city" of Rome, or ab urbe condita (AUC). This was assumed to be 750 BC, although calculations by Marcus Terentius Varro in the 1st century BC determined 753 BC to be the founding date.An alternative system had become more common even by Varro's time, whereby the Romans referred to the names of the consuls rather than the date of the year.References to the year of consulship were used in both conversation and official records. There were two consuls at any one time, and sometimes they each held several terms, meaning that one had to be well educated in history to understand the references. The two systems were compatible; so that the consulship of Quintus Fufius Calenus and Publius Vatinius could be determined as 707 AUC (or 47 BC), the consulship of Caius Julius Caesar (III) and Marcus Aemilius Lepidus as 708 AUC (or 46 BC), and the consulship of Caius Julius Caesar (IV) as 709 AUC (or 45 BC).