Year zero
Historians have never included a year zero. This means that between, for example, and , there are 999 years: 500 years BC, and 499 years AD preceding 500. In common usage "anno Domini" 1 is preceded by the year 1 BC, without an intervening year zero. Neither the choice of calendar system (whether Julian or Gregorian) nor the era ("Anno Domini" or Common Era) determines whether a year zero will be used. If writers do not use the convention of their group (historians or astronomers), they must explicitly state whether they include a year 0 in their count of years, otherwise their historical dates will be misunderstood.
Timeline of Christianity
The purpose of this timeline is to give a detailed account of Christianity from the beginning of the current era (AD) to the present. Question marks ('?') on dates indicate approximate dates.
The year one is the first year in the "Christian calendar" (there is no year zero), which is the calendar presently used (in unison with the Gregorian calendar) almost everywhere in the world. Traditionally, this was held to be the year Jesus was born; however, most modern scholars argue for an earlier or later date, the most agreed upon being between 6 BC and 4 BC.