You put BCE after a year to show it belongs to the time before the birth of Christ — the same stretch of years as BC. 500 BCE is the same year as 500 BC; the count does not change, only the label. The letters stand for Before Common Era (or Before the Common Era). Teachers, museums, and academic books often prefer BCE because it does not put a Christian name on the world’s timeline. In everyday Taiwan school history you may still see BC. The matching label for later years is CE (Common Era), which lines up with AD. Though actually, “Common Era” is a later, more neutral name for a Christian dating system, not a brand-new clock: there is still no year zero, and the line in the sand is still that same traditional year.