QUOTE (Legatus Legionis @ Dec 12 2007, 08:19 AM)

From what I remember, B.C. ( before Christ, correct me if I'm wrong ) is just like a century, 100BC is 100years.
A.D. is Anno Domini ( correct me again if I'm wrong. )
Actually, the designations BC, AD, BCE, and CE are used not to describe a period of years, but the epoch in which the year is counted, measured from the point established for the era's origin.
The Christian Era, Anno Domini ("year of our lord", or AD) was established to be the epoch beginning with the established time of the birth of Christ. Any year forward from that point is designated as ***X AD, and anything before that time is ***X BC. Thus, we are currently in the 2007th year since that established time. Today, we call it the Common Era or CE, in deference to what's already been pointed out.
100 BC, therefore would be the designation not of a century, but a year, 100 years before the beginning of the Christian era, or 2107 years ago.