The Gregorian calendar is the calendar established under the auspices of Pope Gregory XIII in 1582 to replace the Julian calendar. Correcting at a stroke the 10-day accumulated error of the Julian calendar, the main innovation was that century-years were discounted as leap years unless they were divisible by 400. The Gregorian calendar is now used as the civil calendar in most countries. Historical or astronomical dates based on the Gregorian calendar are said to be New Style dates as distinct from Old Style dates that refer to the Julian calendar.