The Battle of Nineveh was the climactic battle of the Byzantine-Sassanid War of 602–628. In mid-September 627, Heraclius invaded Sasanian Mesopatamia in a surprising, risky winter campaign. Khosrow II appointed Rhahzadh as the commander of an army to confront him. Heraclius' Göktürk allies quickly deserted, while Rhahzadh's reinforcements did not arrive in time. In the ensuing battle, Rhahzadh was slain and the remaining Sasanians retreated. The Byzantine victory later resulted in civil war in Persia, and for a period of time restored the (Eastern) Roman Empire to its ancient boundaries in the Middle East. The Sasanian civil war significantly weakened the Sasanian Empire, contributing to the Islamic conquest of Persia.