Battle of Opis — final battle of the Persian conquest of Babylonia

The Battle of Opis was the last major military engagement between the Achaemenid Empire under Cyrus the Great and the Neo-Babylonian Empire, fought in September 539 BC along the Tigris river near the city of Opis. Cyrus had advanced through Mesopotamia following the banks of the Gyndes (the Diyala river), and it was where the Diyala meets the Tigris that his forces routed the Babylonian army. Within days of the Persian victory, Sippar fell without resistance, then Babylon itself opened its gates. The outcome ended the Neo-Babylonian Empire as an independent state and brought its territory into the Achaemenid Empire, which became the largest empire the world had yet seen.

Key facts

  • Country: Iraq
  • Type: battle
  • Date: -539-09
  • Location: Opis

The Setting at Opis

Opis appears in historical records as early as the beginning of the second millennium BC, making it one of the older-attested cities of Babylonia. By the fourteenth century BC it served as the capital of an administrative region, and a royal canal linking the Euphrates and the Tigris terminated near the city. Its strategic value in 539 BC was still greater: Opis sat at one end of the Median Wall, a fortified defensive barrier north of Babylon that Nebuchadnezzar II had built. Any force that controlled Opis and pierced that line would have an open road to the Babylonian capital.

The conflict between Persia and Babylonia may have begun as early as the winter of 540 BC, meaning the engagement at Opis was probably the final stage of an ongoing series of clashes rather than a sudden, isolated confrontation. Cyrus followed the Gyndes south into the heartland of Babylonia, and the armies met near the confluence with the Tigris.

The Battle and Its Immediate Aftermath

The Nabonidus Chronicle places the battle in the month of Tashritu, specifying the location as Opis on the bank of the Tigris. Belshazzar, son of the Babylonian king Nabonidus and crown prince, is traditionally assumed to have commanded the Babylonian forces, though his precise fate after the engagement is not clearly recorded in any chronicle.

After the Persian victory the Chronicle records that a massacre took place at Opis. Scholars disagree on who the victims were: some read the text as referring to the Babylonian army in retreat, others as pointing to the civilian population of the city. What is clear is that the sack of Opis was one of the rare instances in Cyrus’s campaigns where Persian forces engaged in punitive destruction, standing in stark contrast to what followed at Babylon.

Gobryas, identified by scholars as a former Babylonian provincial governor who had defected to Cyrus and brought with him the territory of Gutium as a strategic base, led the Persian army into Babylon. On the fourteenth day of Tashritu, approximately 10 October 539 BC, Sippar was taken without battle and Nabonidus fled. On the sixteenth day, approximately 12 October 539 BC, Gobryas and the army of Cyrus entered Babylon without a fight. Nabonidus was afterwards arrested when he returned to the city.

Consequences for the Ancient World

With Babylon in Persian hands, Cyrus was proclaimed king of Babylonia and all its subject territories, formally ending Neo-Babylonian independence. The incorporation of Babylonia into the Achaemenid state gave Cyrus control over one of the wealthiest and most densely administered regions of the ancient Near East.

Gobryas’s role in the sequence of events illustrates how the Persian advance was facilitated not only by military force but also by defection from within the Babylonian administrative structure. His previous governorship and knowledge of the region gave the Persian army the territorial foothold it needed in Gutium before moving on Opis and then Babylon itself.

The Primary Source: The Nabonidus Chronicle

Virtually everything known about the specific dates and sequence of the fall of Babylon derives from the Nabonidus Chronicle tablet, which was unearthed in 1879 by Hormuzd Rassam during excavations in the Babylon region and acquired by the British Museum from the dealers Spartali and Co. Because Rassam did not record the precise findspot, the archaeological context of the tablet is lost.

The tablet itself is thought to be a Seleucid-era copy, probably produced in the fourth or third century BC, of an earlier document. It was not written immediately after the events of 539 BC it describes, a gap that scholars keep in mind when weighing its precision.

Did you know

  • The Cyrus Cylinder, the key propaganda document produced after the battle’s outcome, did not acquire its modern reputation as a “first charter of human rights” until the late 1950s. It was promoted as such partly to support the Shah of Iran’s political legitimacy, a project that culminated in its adoption as the official symbol of the 2,500th anniversary of the Persian monarchy in 1971. (archive.asia.si.edu)
  • Berossus, a Babylonian historian writing in the third century BC, recorded that Nabonidus was spared by Cyrus after the Battle of Opis and died in exile. That account differs sharply from the violent end often depicted in later traditions. (historycollection.com)
  • The Nabonidus Chronicle tablet, the principal source for the Battle of Opis, is thought to be a Seleucid-era copy (probably fourth to third century BC) of an earlier document, not a tablet inscribed immediately after the events of 539 BC that it describes. (hebrewexplorer.com)

Data sources

Data updated: 2026-10-27