preJulian

PreJulian, also written pre-Julian, is a term used to describe calendars that were in use before the introduction of the Julian calendar by Julius Caesar in 45 BCE. In scholarly contexts it encompasses the various lunar and lunisolar systems that prevailed in the ancient Italic world and neighboring cultures prior to the standard solar-year system.

The most prominent example is the Roman Republican calendar, which developed from an early lunar scheme into a year of about 355 days. It relied on an intercalary month inserted by the pontiffs to keep the calendar aligned with the seasons. Because intercalations were irregular and subject to political manipulation, the calendar drifted with respect to the solar year, causing periodic reform pressures in the late Republic.

Caesar's reform introduced the Julian calendar: a solar year of 365 days with a leap year every four years, a fixed month structure, and a simpler, more regular system of dating. The Julian calendar spread across the Roman world and remained standard in Europe until the Gregorian reform of 1582.

In modern scholarship, the term preJulian is used mainly to distinguish dates and events from calendars that preceded the reform. For astronomical purposes, scholars often use the proleptic Julian calendar to extend Julian rules backward beyond its historical adoption.