The ancient Romans counted from the founding of Rome, 753 B.C.E (Before the Christian Era). That year was called 1 A.U.C. (Anno Urbis Conditae, Latin for the year the city was founded).

The ancient Greeks started counting from the start of the reign of King Seleucus, 312 B.C.E.

According to the old Jewish calendar, the world began in 3760 B.C.E. It is a lunar calendar of 354 days, but a leap year month is added 7 times every 19 years to match the solar year.

Muslims date their calendar from the year Mohammed went from Mecca to Medina, 622 C.E., but they use a lunar year of 354 days, with alternating 29- and 30-day months.

Anglican Bishop calculated that the world was created in 4004 B.C.E.

Most Christians believe that Jesus Christ was born in the year 0, and the world’s calendars are based on this date. Charlemagne, the first Holy Roman Emperor, decreed that years would be counted from this date rather than the founding of heathen Rome.

However, in 535, a Christian scholar, Dionysius Exiguus, calculated that Jesus was born 538 years earlier, or 3 B.C.E.

A later reading of the Bible puts the date of the birth of Jesus somewhere between 20 B.C.E and 4 B.C.E.

For more information about calendars, go to:

http://astro.nmsu.edu/~lhuber/leaphist.html

http://www.calendarzone.com/Historic/