Common Era (also Current Era or Christian Era), abbreviated as CE, is an alternative designation for the calendar era originally introduced by Dionysius Exiguus in the 6th century, traditionally identified with Anno Domini (abbreviated AD). Dates before the year 1 CE are indicated by the use of BCE, short for Before the Common Era (likewise with CE, sometimes, Before the Current Era or Before the Christian Era). Neither designation uses a year zero, and the two designations are numerically equivalent; thus "2018 CE" corresponds to "AD 2018" and "399 BCE" corresponds to "399 BC".