Historically, what was the Hebrew Year when the current year numbering was adopted?

Having a hard time googling this.

I understand that the Hebrew calendar was gradually standardized and adopted among global Jewry over hundreds of years, but here is what I am wondering:

It is currently 5781, so what was the year in which we started counting up to that?

This site claims that it was Maimonedes that determined the Hebrew year in the 12th century, and at that point, he had to count backwards to what he determined to be the year of creation. Does anybody know which year it was that he carried out this work, or if it was even him who did this in the first place? I would love a link to an article or something.

Thanks in advance!