How could dates of birth be calculated before birth of Christ as it could not be known beforehand.

Question

Dates of birth of philosophers such as Plato & Aristotle are circa 600 - 500 B.C. (or B.C.E.), for example. Since it could not have been known beforehand when Christ would be born, how could these dates of birth been established?

Answer 1

Historians who specialize in the period of history known as 'Ancient' - roughly 3000 B.C. / B.C.E. to 500 A.D. / C.E. - have been able to reconstruct a chronology by using the various surviving records of the reigns of kings. emperors, and other leaders of different civilizations. Once historians determined which Roman Emperor(s) ruled during the time in which Jesus lived, they could work backwards, following the reigns of different rulers of different civilizations to construct a timeline. From there, they can use the surviving information about a particular Classical Greek philosopher that indicates under what leaders they lived to determine how long before the birth of Jesus the philosopher in question lived..

As a hypothetical example - in other words, an example that is not necessarily correct, but illustrates what I'm describing - lets say that we know, from the different records of the reigns of rulers, that the city-state of Athens was led by Pericles from the years 429 to 416 B.C. / B.C.E. - from four hundred and twenty-nine years before the birth of Jesus to four hundred and sixteen years before the birth of Jesus. In turn, a surviving account relates that the philosopher Socrates was twenty-six years old in the third year of Pericles' reign as Athens' leader. Assuming this information is correct, then Socrates was twenty-six years old in the year 426 B.C. / B.C.E. Therefore, Socrates would have been born in 452 B.C. / B.C.E.