I understand that the methods works as so
2 BC, 1 BC, 0, 1 AD, 2 AD.
the only thing I don't get is what event was so imporant that someone or some group of people decided to start counting years differently.
I'm aware that the birth of christ is a possibility but i'm looking for possible other answers because Jesus is believed to be born from about 7-4 BC due to the alignment of the Reign of King Herod.
EDIT Question was not worded very well; seemed like a troll. but i'm actually looking for answers.
Not sure if troll, but I'll bite.
Let's say, you have a appointment at the doctor due to August 10th. Let's assume August 10th is the new "zero".
August 12th will be two days since the original date, so it'll be "2 days after August 10th". August 13th will be "3 days after August 10th" and so on.
August 8th would be "2 days before August 10th" and August 9th would be "1 day before August 10th"
If we put in order, it would be (assuming B.A. is "Before August 10th" and A.A. is "After August 10th): 2 B.A.; 1 B.A.; 0; 1 A.A.; 2 A.A. etc
TL;DR: It's a simple mathematics question. The birth of jesus is "year 1"
Ok, based on your other comments, it sounds like what you are confused about is why AD/BC starts when it does, if Jesus was in fact born 4 BC or earlier. This is simply because Dionysius Exiguus who 'came up with' the AD system for numbering, miscalculated and considered 1AD the year of Jesus birth. Actually, he doesn't quite say this, but that was the understanding that emerged. But, once this was in place, and the mistake was made, it was very difficult to change, which is why 'nothing in particular' happened in 1AD.
hi! FYI, you'll find lots more on this in the FAQ (link on sidebar), including a link to an /r/AskHistorians podcast :