The Romans used a system which counted years from the founding of the city:
ab urbe condita (AUC) - 753 BC.
Years would also be named after the two consuls that served that year.(for example, the year of Scipio and Longus)
Hiya, you may be interested in the first couple of sections in the FAQ
The first section is about the Gregorian calendar - the one you're referring to - and includes information on the origin of AD and BC. The second section includes a few examples of other / older dating systems.
These posts have been archived by now, so if you have follow-up questions for any of the users, just ask them here and tag their username to notify them.