Now, we write 2016 because that is 2,016 years AD. Rhe ancient civilizations had no idea that Jesus would have been born and they never referred to themselves as being in "whatever year" BC. So to sum it up, if someone become Christ's time was to write the date, what year would they write?
what year would they write?
If they lived anywhere in the roman world they would have used the Julian version of the roman calendar which made the year 1 AD equal to 754 AUC (AUC is an abbreviation of "ab urbe condita" which means roughly "From the founding of the city [of Rome]".)
However, most Romans would not have given this as a reference to which year it was, the norm was to reference the year by which consuls held office.
There were different systems in different societies. Frequently years were reckoned according to the reign of the current ruler ("In the fifth year of the reign of King Frothingslosh III").
In China (to oversimplify somewhat), up until the Ming dynasty (began 1368), emperors declared "regnal eras" with names that could change during the life of the emperor. For example, the second emperor of the Song Dynasty, Song Taizong, who ruled from 976-997, had five different regnal eras during his time on the throne, each with a different name, and each resetting to "year 1 of the _____ era" at its beginning.
These names were usually chosen for their auspicious or propagandistic implications. The first Ming emperor, for example, who gained power by military force during the expulsion of the Mongols from China, called his reign "Hongwu," "immensely military," or, as one contemporary European poetically translated it, "a fludde [flood] of arms" ("hong" can literally mean "flood").
This system is still used, after a fashion, in Taiwan, where government documents refer to 2016 as "the 105th year of the Republic" (rather than "of some emperor's reign"). Presumably this will never reset to Year 1 because the Republic, unlike an emperor, is (supposedly) immortal.
Japan still uses a reign-name-and-year system for some official or traditional purposes, too. Hirohito's reign name was "Showa," meaning "Bright Harmony/Peace" (which didn't turn out to be particularly apt). The current emperor's reign is "Heisei" ("complete/universal peace")