The Gregorian calendar.
The main calendar on this website is the Gregorian calendar
, also called the Western calendar and the Christian calendar.
This is the most widely used calendar in the world today. The Gregorian calendar dates back to 1582 and was introduced by Pope Gregory XIII, after whom the calendar was named. The calendar was based on the Julian calendar which dates back to 46 BC. The main difference between the Gregorian and the Julian calendar is the frequency of leap years.
The Julian calendar.
The Julian calendar was a reform of the Roman calendar and was introduced by Julius Caesar in 46 BC. The Julian calendar
has 365 days divided into 12 months, and has a leap day added every four years. This calendar was the dominant calendar in most of Europe for more than 1500 years until it was replaced in 1582.
The Roman calendar.
This calendar dates back to the founding of the Roman Empire in 753 BC. The calendar is believed to be based on of the Greek lunar calendars. A lunar calendar divides the year up according the cycles of the moon, which at the time was 29.5 days. The original calendar is believed to have had only 10 months, with January and February being added in a reform by Numa Pompilius in 713 BC. This calendar went through many reforms until the most well known reform by Julius Caesar in 46 BC.