Nabû-nāṣir (simplified in English as Nabonassar) was the king of Babylon from 747 to 734 BC. He deposed a foreign Chaldean usurper named Nabu-shuma-ishkun, bringing native rule back to Babylon after twenty-three years of Chaldean rule. His reign saw the beginning of a new era characterized by the systematic maintenance of chronologically precise historical records. Both the Babylonian Chronicle and the Ptolemaic Canon begin with his accession to the throne. He was contemporary with the Assyrian kings Aššur-nirarī V (755–745 BC) and Tiglath-Pileser III (745–727 BC), under the latter of whom he became a vassal, and the Elamite kings Humban-Tahrah I (reigned until 743 BC) and Humban-Nikaš I (742–717 BC). may have been composed during his reign as it records the succession of kings from the antediluvian era down to his immediate predecessor, Nabû-šuma-iškun. It records that the "dynasty of Chaldea was terminated" (with Nabû-šuma-iškun) and "its kingship was transferred," but the remainder is lost. He may also have commissioned a vituperative chronicle which vilifies his predecessor for his sacrilegious actions and the Chronicle of the Market Prices which mentions the volatile costs of various commodities in reigns up until that of his predecessor. His name appears in the Eclectic Chronicle but the context has not been preserved.
Calendar reform
thumb|King's line art for the Eclectic Chronicle, BM 27859, a post-Kassite chronicle of Mesopotamian history
His reign marks the reform of the Babylonian calendar, introducing regular calculated intercalary months, the eighteen-year cycle texts (the 223-month Saros Cycle, named for Edmund Halley’s misreading of a passage in Pliny) and perhaps even the zodiac. Berossus of Kos reported, in an account preserved by Syncellus, that it was from the reign of Nabû-nāṣir onward that the movements and duration of the stars were recorded. He noted in his work Babyloniaca that: "He gathered the records of his predecessors and destroyed them, thus ensuring that the history of the Chaldean kings began with him."
According to Claudius Ptolemy in his work Almagest, this gave rise to an era beginning at noon on 26 February 747 BC, when the Anno Nabonassari began, but prior to the Hellenistic period there is no trace of this era. The Babylonian Chronicle, although the earliest exemplar of these dates to 652 BC. started with the lunar eclipse of 747–746 BC (6 February 747 BC according to Britton), a spectacular conjunction of the moon and the planets which may have inspired the commencement of recording of accurate astronomical observations.
Whether or not he actually solicited military aid from the Assyrians, Nabû-nāṣir seems to have been the main beneficiary of these actions as his regime was stabilized and he was subsequently able to put down a revolt in Borsippa. commemorating their own restorations, usurping monarchic privilege.
Economic activity
Twenty-three tablets survive dealing with agricultural production, animal husbandry, weaving and sales from his first to his fourteenth year
He is recorded as having succumbed to illness and died in his palace during the fourteenth year of his reign.