Battle of Opis

The Battle of Opis was the last major military engagement between the Achaemenid Empire and the Neo-Babylonian Empire, which took place in September 539 BC, during the Persian invasion of Mesopotamia. At the time, Babylonia was the last major power in Western Asia that was not yet under Persian control. The battle was fought in or near the strategic riverside city of Opis, located north of the capital city of Babylon in modern-day Iraq, and resulted in a decisive victory for Persia. Shortly afterwards, the Babylonian city of Sippar surrendered to Persian forces, who then supposedly entered Babylon without facing any further resistance. The Persian king Cyrus the Great was subsequently proclaimed as the king of Babylonia and its subject territories, thus ending its independence and incorporating the entirety of the fallen Neo-Babylonian Empire into the greater Achaemenid Empire.

The battle took place in and around Opis, an ancient city situated on the Tigris River and located about 80 kilometres (50 mi) north of Baghdad in modern-day Iraq. The city is thought to have been a preferred point to cross the Tigris; the classical Greek philosopher Xenophon describes a bridge at this point. The timing of the Persian invasion may have been determined by the ebb of the Mesopotamian rivers, which are at their lowest levels—and therefore easier to cross—in early autumn.

Opis was a place of considerable strategic importance; apart from the river crossing, it was at one end of the Median Wall, a fortified defensive barrier north of the ancient city of Babylon that had been built several decades earlier by the Babylonian king Nebuchadnezzar II. Control of Opis would have enabled the Persians to break through the Median Wall and open the road to the Babylonian capital.

The main contemporary source of information on Cyrus's Mesopotamian campaign of 539 BC is the Nabonidus Chronicle, one of a series of clay tablets collectively known as the Babylonian Chronicles that record the history of ancient Babylonia. Some additional detail is provided by one of the few documents to have survived from Cyrus's lifetime, the Cyrus Cylinder. Further information on Cyrus's campaign is provided by the later ancient Greek writers Herodotus and Xenophon, though neither mention the battle at Opis and their accounts of the campaign differ considerably from the Persian and Babylonian sources. Most scholars prefer to use the Nabonidus Chronicle as the main source on the battle, as it is a contemporaneous source.

Although much of the Nabonidus Chronicle is fragmentary, the section relating to the last year of Nabonidus's reign – 539 BC – is mostly intact. It provides very little information about Cyrus's activities in the years immediately preceding the battle. The chronicler focuses on events of immediate relevance to Babylonia and its rulers, only occasionally records events outside Babylonia and does not provide much detail other than a bare outline of key incidents. There is almost no information for the period 547–539. Most of the chronicle's text for this period is illegible, making it impossible to assess the significance of the few words that can be read.

At the time of the Battle of Opis, Persia was the leading power in the Near East. Its power had grown enormously under its king, Cyrus II, who had conquered a huge swathe of territory to create an empire that covered an area corresponding to the modern countries of Turkey, Armenia, Azerbaijan, Iran, Kyrgyzstan and Afghanistan. The only remaining significant unconquered power in the Near East was the Neo-Babylonian Empire, which controlled Mesopotamia and subject kingdoms such as Syria, Judea, Phoenicia and parts of Arabia. It had been closely linked with Cyrus's enemies elsewhere. The empire was previously an ally of Croesus of Lydia, whose kingdom was overrun by the Persians a few years prior to the invasion of Babylonia.

By the time of the battle, Babylonia was in an unpromising geopolitical situation; the Persian empire bordered it to the north, east and west. It had also been suffering severe economic problems exacerbated by plague and famine, and its king Nabonidus was said to be unpopular among many of his subjects for his unconventional religious policies. According to Mary Joan Winn Leith, "Cyrus's success is credited to military acumen, to judicious bribery, and to an energetic publicity campaign waged throughout Babylonia, which portrayed him as a lenient and religiously tolerant overlord." On the other hand, Max Mallowan notes: "Religious toleration was a remarkable feature of Persian rule and there is no question that Cyrus himself was a liberal-minded promoter of this humane and intelligent policy," and such a publicity campaign was in effect a means of permitting his reputation to precede his military campaign. Cyrus was said to have persuaded a Babylonian provincial governor named Gobryas (and a supposed Gadates) to defect to his side. Gutium, the territory governed by Gobryas, was a frontier region of considerable size and strategic importance, which Cyrus was said to have used as the starting point for his invasion.

The Nabonidus Chronicle records that prior to the battle, Nabonidus had ordered cult statues from outlying Babylonian cities to be brought into the capital, suggesting that the conflict had begun possibly in the winter of 540 BC. In a fragmentary section of the chronicle which is presumed to cover 540/39 BC, there is a possible reference to fighting, a mention of Ishtar and Uruk, and a possible reference to Persia. The Battle of Opis was thus probably only the final stage in an ongoing series of clashes between the two empires.