Why did time count backwards before the birth of Christ?

Answer 1

In ancient times, years were counted forwards from the beginning of the king's reign. We see this in the biblical books of Kings and in other records from the times.

In what is now 533, the Roman abbot Dionysus Exiguus set out to develop a new calendar, based on the start of Christianity. He knew that it was impossible to say when Jesus was born, but he knew, or thought he knew, when Herod died. So, he devised the new Christian calendar to begin on the year of Herod's death. He based the date of Herod's death on the reign of the Roman emperor Augustus, but was unaware that Augustus only adopted that name four years after his reign began, going by his birth name of Octavius until then. So, Exiguus commenced his calendar just 4 years too late.

However, the proposed new calendar was only adopted in Western Europe after it was used by the Venerable Bede to date the events in his Ecclesiastical History of the English People, completed in 731.

So, we now date events from before the advent of Christianity backwards, because of the work of Dionysus Exiguus, but this was not how the people of those times understood it. They dated events forward from some event that was important to them.