Why does the western calendar start with the birth of Christ?
Math and Calendars in History
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The story behind the western calendar—the one that developed into the calendar most often used today—started in the middle of the 6th century. Pope St. John I asked Dacian monk and scholar Dionysius Exiguus (“Dennis the Small,” c. 470-c. 540; born in what is now Romania) to calculate the dates on which Easter would fall in future years. Dionysius, often called the inventor of the Christian calendar, decided to abandon the calendar numbering system that counted years from the beginning of Roman Emperor Diocletian’s reign. Instead, being of Christian persuasion, he replaced it with a system that started with the birth of Christ. He labeled that year “1,” mainly because there was no concept of zero in Roman numerals.