The Battle of Nineveh was the deciding battle of the Byzantine-Sassanid War of 602–628. The Byzantine victory broke the power of the Sassanid dynasty and for a period of time restored the empire to its ancient boundaries in the Middle East. This resurgence of power and prestige was not to last, however, as within a matter of decades an Arab Caliphate emerged from Arabia and once again brought the empire to the brink of destruction.

In mid-September 627, leaving Ziebel to continue the siege of Tiflis, Heraclius invaded the Persian heartland, this time with between 25,000 and 50,000 troops and 40,000 Göktürks. The Göktürks, however, quickly deserted him because of the strange winter conditions. Heraclius was tailed by Rhahzadh's army of 12,000, but managed to evade Rhahzadh and invaded the heartland of the Persian Empire, in Mesopotamia (modern Iraq). Heraclius acquired food and fodder from the countryside, so Rhahzadh, following through countryside already stripped, could not easily find provisions. This resulted in harm to Rhahzadh's animals.

Rhahzadh deployed his forces into three masses and attacked. Heraclius feigned retreat to lead the Persians to the plains before reversing his troops to the surprise of the Persians.[1] After eight hours of fighting, the Persians suddenly retreated to nearby foothills, but it was not a rout. 6,000 Persians fell.

Nikephoros' Brief History tells that Rhahzadh challenged Heraclius to personal combat. Heraclius accepted and killed Rhahzadh in a single thrust; two other challengers fought and also lost. In any case, Rhahzadh died sometime in the battle.

The 3,000 Persian reinforcements arrived too late for the battle. This victory was significant enough to shatter the resistance of the Persians.

Khosrau II was overthrown, raising his son Kavadh II, also known as Siroes, in his stead. Khosrau perished in a dungeon after suffering for five days on bare sustenance—he was shot to death slowly with arrows on the fifth day. Kavadh immediately sent peace offers to Heraclius. Heraclius did not impose harsh terms, knowing that his own empire was also near exhaustion. Under the peace treaty, the Byzantines regained all their lost territories, their captured soldiers, a war indemnity, and of great spiritual significance, the True Cross and other relics that were lost in Jerusalem in 614. The battle marked the end of the Roman-Persian Wars.