https://history.info/on-this-day/1582-introduction-of-the-gregorian-calendar/#:~:text=Gregory%20XIII%20conducted%20a%20reform%20of%20the%20calendar,the%20reforms%20were%20Christopher%20Clavius%20and%20Aloysius%20Lilius.
https://history.info/on-this-day/1582-introduction-of-the-gregorian-calendar/#:~:text=Gregory%20XIII%20conducted%20a%20reform%20of%20the%20calendar,the%20reforms%20were%20Christopher%20Clavius%20and%20Aloysius%20Lilius.