• Index
• Overview
• Ancient Calendars
• The Roman Calendar
• The Gregorian Calendar
• Religious Calendars

In AD 325, the year of the First Council of Nicaea, Pope Gregory XIII issues a decree dropping 10 days from the Julian calendar. He instituted a calendar named after himself, that provided that century years divisible evenly by 400 should be leap years and other century years should be common years. It was slowly adopted all over Europe and used today in most of the Western World and in parts of Asia. When the new calendar was adopted by Great Britain in 1752, changes were made.

1. The day after Sept. 2, 1752 became Sept. 14
2. Adopted January 1 as the day when a new year begins.

The Gregorian calendar is also called the Christian calendar because it uses the birth of Jesus Christ as a starting date. Dates of the Christian era are often called AD (Latin anno domini, "in the year of our Lord") and BC (before Christ) Although the birth of Christ was originally given as Dec. 25, 1 BC, modern scholars now place it about 4 BC .