The current Anno Domini system was invented by Dionysius Exiguus in 525 AD (too bad a miscalculation missed the real Year 1 by a few years .. but that is past the point of fixing). Most scholars believe a date of birth for Jesus between 6 BC and 4 BC.

On to your question: this numbering system wasn't widely used until 800 AD (the year that pope crowned Charlemagne emperor at St. Peter’s Basilica) but its adoption varied by country.