Obviously the entirety of human history wasn't counting backwards until some random kid was born. So how were years tracked at that point, if at all? Were they retroactively changed? Was there a "Year 1" of human history before then? Everything now is centered around the BCE/CE split in terms of listing dates and years, and I'm curious how this was done before then, or even after - it's not like the entire world suddenly reset all of their year records to "1" when Jesus was born.