1582 Introduction of the Gregorian calendar
435 years ago, on October 4, 1582, Pope Gregory XIII introduced a new calendar. The next day was declared October 15 in the Italian states, the Commonwealth, Portugal and Spain. In other countries of the Christian world, the Gregorian calendar was introduced later, during the 16th-20th centuries. He made it possible to almost completely eliminate the backlog of the previous, Julian calendar from the astronomical year.