1582 (MDLXXXII) was a common year starting on Monday (link will display the full calendar) of the Julian calendar, and a common year starting on Friday (link will display the full calendar) of the proleptic Gregorian calendar, the 1582nd year of the Common Era (CE) and Anno Domini (AD) designations, the 582nd year of the 2nd millennium, the 82nd year of the 16th century, and the 3rd year of the Proleptic 1580s decade. However, this year also saw the beginning of the Gregorian calendar switch, when the papal bull known as Inter gravissimas introduced the Gregorian calendar, adopted by Spain, Portugal, the Polish–Lithuanian Commonwealth and most of present-day Italy from the start. In these countries, the year continued as normal until Thursday, October 4. However, the next day became Friday