How does BC go backwards or forwards?

BC, or "Before Christ," denotes years before the traditional date of Christ's birth, while AD, or "Anno Domini," refers to years after. In this system, the years count down as they approach year 1 BC (e.g., 2 BC is followed by 1 BC), and then transition into AD, where the years count up starting from AD 1. Thus, the timeline moves backwards in BC and forwards in AD, with no year zero between the two.