Notes and queries: How they counted the years in the BC era; what noise does a giraffe make? | From the Guardian | The Guardian
The Roman calendar was counted Ab urbe condita ("from the foundation of the city"), in 753 BC; and it continued in use until the Anno Domini calendar was introduced in AD 525. The monk who calculated AD from AUC forgot that the Emperor Augustus ruled for four years as Octavian before he changed his name, and this error remains in the system. Also, as he counted in Roman, not Arabic, numerals, he did not include the years 0 BC and AD 0.
The Muslim calendar runs from the Hijra, Muhammad's flight from Mecca to Medina in AD 622. Like the Christian calendar, it displaced earlier calendars such as the Zoroastrian one in Persia, which dates from about 1200 BC. The Muslim calendar is a lunar one, but Iranians still celebrate Nowruz, the new year in the solar Zoroastrian calendar, at the spring equinox each March.
The Chinese calendar dates back to about 2700 BC and the Hindu calendar to about 3100 BC. The Jewish calendar has an even earlier starting point, 5,770 years ago, calculated as the date of the creation as described in scripture.
. . .