are the two most commonly used notations to denote the dates of historical events. However, most ancient civilizations did not use this method of marking dates. The Christian calendar was introduced in Rome only when the converted to Christianity. This system of dating is still used internationally. Using a dating system makes it easier to mark and compare historical events.

Although you did not include options for this question, we can answer the following.

BC and AD or BCE and CE are the two most commonly used notations to denote the dates of historical events. However, most ancient civilizations did not use this method of marking dates. The Christian calendar was introduced in Rome only when the Roman Emperors converted to Christianity. This system of dating is still used internationally. Using a uniform dating system makes it easier to mark and compare historical events.

There is no doubt that history needs a uniform system to date events and incidents in human history. Otherwise, historians could confuse people who misunderstand the events in the context of time.

Then in 1582, Pope Gregory XIII made his contribution and introduced the so-called Gregorian calendar.

These adjustments in the measure of time have helped historians and scholars to properly locate events and match them with characters that were the protagonist of history. So in simple terms, we can refer to common dates and being on the same page.