Well, given that year numbering system's start in Europe, zero wasn't as broadly accepted as other digits at the time. By AD 150, Ptolemy, influenced by Hippar

Well, given that year numbering system's start in Europe, zero wasn't as broadly accepted as other digits at the time. By AD 150, Ptolemy, influenced by Hipparchus and the Babylonians, was using a symbol for zero. https://en.wikipedia.org/wiki/0#History https://en.wikipedia.org/wiki/0#History To keep it confusing: the traditional proleptic Gregorian calendar (like the Julian calendar) does not have a year 0 and instead uses the ordinal numbers 1, 2, ... both for years AD and BC. Thus the traditional time line is 2 BC, 1 BC, AD 1, and AD 2. ISO 8601 uses astronomical year numbering which includes a year 0 and negative numbers before it. Thus the ISO 8601 time line is −0001, 0000, 0001, and 0002. https://en.wikipedia.org/wiki/Gregorian_calendar#Dual_dating https://en.wikipedia.org/wiki/Gregorian_calendar#Dual_dating