Pope Gregory XIII & the Ten Lost Days!

Pope Gregory XIII by Pietro Paolo Olivièri, Santa Maria in Aracoeli

---

Pope Gregory XIII (r. 1572-85) is, perhaps, best remembered for amending the 1600 year old Julian calendar, correcting a 10-day drift, thereby aligning Easter with the spring equinox. 

On February 24th 1582, Gregory XIII issued the bull, Inter gravissimas, which modified the Julian calendar, introduced by Julius Caesar in 46 BCE. The new system refined the use of leap years. A year is a leap year if divisible by 4, except for century years not divisible by 400. For example, 1900 was not a leap year, but 2000 was.

​What came to be known as the Gregorian calendar came into effect later in the same year when October 4th was followed by October 15th, leading many to accuse Gregory XIII of stealing ten days from their lives!

Pope Gregory XIII is interred in St Peter's Basilica. His funerary monument refers to his amendment of the Julian calendar.  

---