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On 12 October 539 BCE of the Julian calendar, the Persian Empire conquered the Neo-Babylonian Empire, according to Biblical scholars William Sanford LaSor, David Allan Hubbard, and Frederic William Bush, with the collapse of the city Babylon to the armies of Cyrus the Great. This is based on chronologies developed from the writings of Haggai and Daniel of the Hebrew Bible as well as contemporary writings such as the chronicles of Nabondius. The fall of Babylon ended the native reign of Mesopotamia, putting it in the hands of the Persians, giving them control over the full Fertile Crescent. It was also done 'without fighting', according to Nabondius' chronicles, as well as by an inscription known as the Cyrus Cylinder.
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The Neo-Babylonian Empire began in 626 BCE with the coronation of Nabopolassar as King of Babylon and firmly established with the fall of the Assyrian empire in 612 BCE. It was the first time in nearly 1000 years that Babylon and the wider area of southern Mesopotamia rose to dominance in the ancient Near East after the reign of Hammurabi, who reigned from about 1792-1750 BCE. It also retains a place in western cultural memory because of the 'invidious portrayal of Babylon and its greatest king Nebuchadnezzar II in the Bible', which focuses on his campaign against the Kingdom of Judah, most notably the siege of Jerusalem and the destruction of Solomon's Temple in 587 BCE. Babylonian sources, in contrast, record 'Nebuchadnezzar's reign as a golden age that transformed Babylonia into the greatest empire of its time'.
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Though the old, or First Babylonian Empire, continued about 150 years after the death of Hammurabi, when it collapsed, Babylon remained a small state afterwards, until it fell to the Hittite king Mursili I (about 1595 BCE, and then was controlled by the Kassites, who ruled it for about 500 years before the native Babylonian rulers deposed them and it remained a 'rump state', a remnant, reduced state, a time known as the 'Middle Babylonian period' when the native Babylonians (descendants of Sumerians and Akkadians, as well as the assimilated Amorites and Kassites) and the newly arrived, unassimilated arrivals from the Levant (Suteans, Arameans, and Chaldeans) formed two separate groups within the cities. Over time, by the 8th century BCE, the two groups were beginning to become a single group, so much so that the major Chaldean tribes had produced at least one Babylonian king by 730 BCE. This isn't to say that they were strong kings, though, with the 9th and 8th centuries BCE being a series of weak kings that failed to control all the groups within the empire, much less defeat their rivals or maintain trade routes. This resulted in in the Neo-Assyrian Empire conquering 729 BCE, leading to the century-long struggle for control over Babylon as it struggled against the 'unstable Assyrian rule, including several unsuccessful Babylonian revolts'.
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In 627 BCE, Sinsharishkun became king of the Neo-Assyrian Empire, though a southern official or genera, Nabopolassar revolted against the general instability of Assyrian rule, at that time exemplified by a civil war between Sinsharishkun and Sin-shumu-lishir, a general and usurper who became ruler of some of the northern cities of Babylon for a few months. In 626, BCE, Nabopolassar was able to seize the cities of Babylon and Nippur. Sinsharishkun was able to recapture Nippur and besieged Nabopolassar in Uruk, but failed to capture Uruk or Babylon. In 626 BCE, Nabopolassar became King of Babylon, 'restoring Babylonia as an independent kingdom after more than a century of Assyrian rule'. Nippur and Uruk soon came under Babylonian rule and the Assyrian Empire began to fall apart by 617, when Sinsharishkun was defeated at Nippur and it fell to other enemies, including the Medes who allied with Babylon, so that it had completely fallen apart by 609 BCE.
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Nebuchadnezzar II succeeded his father Nabopolasser in 605 BCE, inheriting one of the 'most powerful [empires] in the world' and he married the Median king's daughter Amytis, for whom he built the Hanging Gardens of Babylon, though this is debated. He ruled for 43 years and was king of 'the most powerful kingdom in the Middle East'. He conquered the Levant after a series of wars and campaigns early in his reign. He even laid siege to Tyre, a city in modern-day Lebanon for 13 years, an island about 700 meters off-shore. While he was unable to conquer the city due to not having a navy, he was able to make them agree to be ruled by vassal kings. The city wasn't actually captured until Alexander the Great laid siege to it in 332 BCE. This gave him control over the Fertile Crescent. Nebuchadnezzar might have campaigned against Egypt, as well, in 5568-567 BCE, but the record is fragmentary. Modern research suggests that they were initially successful then repelled by Pharaoh Amasis II.
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Nabonidus became king of the Neo-Babylonian Empire on 25 May 556 BCE, the son-in-law of Nebuchadnezzar II, taking the throne as the sixth king of the Neo-Babylonian empire, about six years after the death of Nebuchadnezzar II, the second king of Neo-Babylonian empire. He was also the father of Belshazzar, who is also mentioned in the Hebrew Bible. His assent to the throne was likely the result of his son Belshazzar leading a revolt against his predecessor Labashi-Marduk, to his apparent surprise. He apparently sought to raise the moon god Sin over the national deity Marduk, apparently wanting make Sin the head of the entire Mesopotamian pantheon, though how much religious reform was actually made is debated. While Nabonidius fought against the prince of Tayma and was in self-imposed exile during 552-543/542 BCE, Belshazzar acted as regent in Babylonia. Upon Nabonidus' return to Babylonia, he rebuilt Eáž«uláž«ul, a temple dedicated to Sin in Harran, now a district of Ćanlıurfa Province, Turkey, a major city of the northern part of the empire. Based on the inscription left on his mother's, Adad-guppi, grave, he had great-grandchildren early in his reign, given she claimed to have great-great-grandchildren and it's thought that he was her only surviving child, if not her only child.
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It's thought that Nabonidus was 'mad, on account of his religious policies', an idea that filtered through the Hellenistic and Jewish traditions, with some thinking that the Book of Daniel re-attributed his 'madness' to Nebuchadnezzar II, though no cuneiform sources mention this madness of Nabonidius or Nebuchadnezzar, though one account, known as the Verse Account, critiques Nabonidius' religious reforms and even though this account hails Cyrus the Great as a 'liberator rather than conqueror', it does not question Nabonidius' sanity. Even accounts, such as by Berossus, a Hellenistic-era Babylonian writer and priest of Bel Marduk who wrote around 290-278 BCE, that present Nabondius as a usurper, which Nabonidius admitted himself, but didn't record any negative assessments of him as a king. Had he been considered mentally unstable, it is unlikely that he would have kept the throne, nor would later Babylonian rebels claimed to be his sons.
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As Marduk chief cult center was Babylon, the priests of Mardok became increasingly disaffected with Nabonidus' insistence on elevating Sin above Marduk. The military also became disaffected with him as he preferred his studies, leaving defense of the empire to Belshazzar, who was an 'capable soldier but poor diplomat who alienated the political elite', and spent a great deal of time out of Babylon. In the 6th year of his reign, Cyrus the Great gained the throne of Persia and put down an Assyrian revolt in 547 BCE while Nabonidus was in a camp in Arabia, near the southern frontier of his kingdom, which led Belshazzar in charge of the defenses against Cyrus. By 540, the vast majority of Babylon's eastern territory was under Cyrus and his armies were pressing into Syria, with many of Nabonidus' vassals being placed under Cyrus' authority. When Nabonidus returned to Babylon in 543 BCE, Cyrus was constantly pushing against the border of the Babylonian Empire.
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Exactly what happened in 539 BCE is difficult to reconstruct due to inconsistencies between the various records of the time. The Cyrus Cylinder, which is an Achaemenid royal record described Babylon being taken 'without battle' while Herodotus and Xenophon, both Greek historians, record the city was besieged. The Book of Daniel reports that Belshazzar was killed, which was recorded by Xenophon, but not widely accepted by modern scholars. Nabonidus surrendered and was summarily deported while Gutian guards were set at great temple of Bel and the gates of the city. Cyrus arrived either on the 28th or 29th of October and made Gobryas, one of his generals who had been in charge of subduing the city, governor of the province of Babylon.
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While Babylon moved people from their homelands, a policy known as 'population transfer', Cyrus allowed people to return to their homelands, carrying their sacred items with them. He also allows the priests of Marduk to declare him king of Babylon, portraying himself as the savior and 'legitimate successor of the ancient Babylonian kings', portrayed by the priests of Marduk as the tool used against the 'impiety of Nabonidus who had moved the images of the local gods from their ancestral shrines'.