Anno Mundi
Anno Mundi (Latin: "in the year of the world") abbreviated as AM or A.M., refers to a Calendar era counting from the creation of the world.
Jewish computation
Years in the Hebrew calendar are counted from the creation year. The system in use today was adopted as early as the 3rd century CE, and based on the calculation in the Seder Olam Rabbah of Rabbi Yose Ben Halafta in about 160 CE.
By his calculation the earth was created in the year 3761 BCE. The Jewish year spanning 2007–2008 CE, after Rosh Hashanah, is 5768 AM in the Hebrew calendar.
Other computations
AM was also used by early Christian chronographers. The medieval historian Bede dated creation to 18 March 3952 BC. The Irish Annals of the Four Masters dated creation to the year 5194 BC.
The Aetos Kosmou is the corresponding concept in the Byzantine calendar, which dates creation to 1 September, 5509 BC.
James Ussher (1654) dated creation to 23 October, 4004 BC.
Related to this is the Anno Lucis of Freemasonry, which adds 4000 years to the AD date; and the Julian day number, counting the days that have elapsed since noon Greenwich Mean Time (UT or TT) on Monday, January 1, 4713 BC.
The date inferred from the Roman Martyrology[1] is 25 March, 5199 BC, which is close to the date of the Irish annals mentioned above.
References
See also Floyd Nolan Jones work on Creation of the World date