The Beginning of Traceable Chronology
By Atul Bishnoi - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=35391210
Figuring out when something happened in the records that ancient people left is complex since each civilization tended to count years based on the reign of their rulers, along the lines of 'in the X year of Y, this happened'. It was also common for kings to destroy the records of those they replaced or conquered. Finding mention of one king's reign beginning or ending in the chronicles of another kingdom allows some inference about when things happened. Our modern, global calendar is a relatively modern invention and many places use their own calendar alongside the Gregorian calendar.
Nabû-nāṣir was a Babylonian king who reigned from 26 February 747 BCE. We know this because he reformed the calendar by aligning the Babylonian calendar to have regular 'extra' months to align the lunar and solar calendars, the beginning of the calculated Saros Cycle, which allows us to predict or date solar and lunar eclipses which have a 223 month cycle, and maybe even standardized the zodiac. He recorded this in the Babylonian Chronicle, which continued to be used until 668 BCE. Despite not having a particular systemic model of the cosmos, the Babylonians were extremely good at calculating regular events in the night sky.
By L. W. King - Chronicles Concerning Early Babylonian Kings, Vol. II: Texts and Translations, pp. 147-155, Public Domain, https://commons.wikimedia.org/w/index.php?curid=23227587
The Canon of Kings was used by astronomers to record their observations. It was kept from Nabû-nāṣir's reign through to 160 CE. It was continuous except for two periods when there were no kings, between Sargon II and Bel-ibni in 704-703 BCE and then between Meshezib-Marduk and Esarhaddon 688-681 BCE. It then moved through the Persian kings (538-332 BCE), the Macedonian Greek Kings (331-305 BCE), then into Egypt during the Ptolemies (304-30 BCE) and then to the Romans (29 BCE - 160 AD).
By Theodor de Bry - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=67098
Cladius Ptolemy lived in Hellenistic Egypt from about 100 CE to about 170 CE. He wrote about a dozen treatises on mathematics, astronomy, astrology, geography, and music theory. One of his books, known now as Almagest (اَلْمَجِسْطِيّ, al-majisṭī, 'the greatest'), but originally known as Mathematical Treatise (Μαθηματικὴ Σύνταξις, Mathēmatikḕ Sýntaxis). It was preserved by Arab scholars after the fall of the Western Roman Empire and was used until Copernicus' theory of heliocentrism replaced Ptolemy's geocentric theory of the cosmos, which was outlined in the book. The Greeks used the mathematics of the Babylonians and developed a theory of the way things were arranged. Despite his cosmological theory being replaced, his chronology is still used.













