Byzantine–Sasanian War of 602–628

In 602 the Byzantine army on the Danube mutinied and raised the centurion Phocas to the throne, and Maurice was killed. Khosrow II, who owed his crown to Maurice, declared war to avenge him, and the general Narses, who had risen against Phocas at Edessa, called on the Persians for help. Dara fell in 605, and while Byzantium was torn by the revolt of the Heraclii against Phocas (608–610) the Persians took Amida, Edessa and the cities of Armenia. Heraclius, emperor from 610, could not stop them: in 613 he was defeated near Antioch, Damascus fell, and after further defeats in Cilicia the empire was cut in two. In 614 the Persians, joined by Jewish rebels, took Jerusalem after a siege of about three weeks. According to the sources, churches, among them the Holy Sepulchre, were burned, although excavations have not confirmed widespread destruction; many inhabitants were killed or deported — estimates of the dead range from a few thousand to tens of thousands — and the True Cross was carried off to Ctesiphon. Egypt, the granary of Constantinople, was conquered in 618–621 (the invasion is dated to 618, by other accounts to 616 or 617; Alexandria fell in 619), and Persian armies reached Chalcedon on the Bosporus.

Heraclius rebuilt his army with loans of church treasure and from 622 took the offensive. In 624 he marched through Armenia into Atropatene and destroyed the great fire temple of Adur Gushnasp. In 626 Khosrow tried to end the war at a stroke: a Persian army under Shahrbaraz encamped at Chalcedon while the Avars and Slavs besieged Constantinople from the European side, but the Byzantine fleet kept the allies apart and the siege failed. Allied with the Western Turks, Heraclius invaded Mesopotamia in September 627 and on 12 December defeated the Persian army near the ruins of Nineveh. The royal palace of Dastagird was plundered; in 628 a coup overthrew Khosrow in favour of his son Kavad II (Sheroe), who had him killed and made peace, restoring to Byzantium its lost provinces, its prisoners and the relics taken from Jerusalem. Heraclius brought the True Cross back to Jerusalem, by the usual dating on 21 March 630 (by other accounts twice, in 629 and 630).

The war, fought across the whole Near East, left both empires ruined: the Balkans had largely passed to the Slavs, Anatolia had been devastated by repeated invasions, and the Sasanian state fell into a civil war in which about ten kings and queens followed one another in four years. The Qur’an (Sura 30, al-Rum) alludes to a defeat of the Romans in a nearby land and foretells their victory within a few years, and Muslim commentators linked the verses to this war. Within a few years of the peace the Arabs attacked both exhausted empires — the historian James Howard-Johnston likened their onslaught to “a human tsunami”. The war is known mainly from Byzantine, Armenian and Syriac writers such as the Chronicon Paschale, George of Pisidia, the history attributed to Sebeos and Theophanes, since the Persian archives are lost.