Gregorian Calendar (Reform of 1582)

Timeline

1. 1572–1582Rome · LazioSince the Julian calendar's introduction, the date of the spring equinox had gradually drifted relative to the Easter computation; in the 1570s the pope commissioned Clavius and others, who confirmed that ten days must be deleted and the leap-year rules revised to correct the accumulated error.
2. 1582Rome · LazioGregory XIII issued the bull Inter gravissimas in February 1582; after Thursday, October 4, the date jumped directly to Friday, October 15, deleting ten days; the new leap-year rule was a leap year every four years, except for century years, with a leap year again every 400 years.
3. 1582–1700Spain · SpainCatholic countries such as Italy, Spain, Portugal, and Poland–Lithuania adopted the new calendar successively in the 1580s; Protestant regions resisted for a long time, creating a situation of dual calendars in Europe and increasing the cost of date conversion in cross-border dealings.
4. 1752London · EnglandFrom the 18th to the 20th century, countries successively abandoned the Julian calendar or local calendars in favor of the Gregorian calendar; by the 20th century it had become the international civil standard, supporting unified date expression in navigation, telegraphy, aviation, and globalized commerce.