The Byzantine-Sasanian War of 602-28 was the final and most devastating of the series of wars fought between the Byzantine Empire and Sassanid Persia. The brutal war saw the Persians conquer much of the Caucasus, the Levant, and Egypt before being pushed back by Emperor Heraclius, who decisively defeated the Persians at the Battle of Nineveh in 627. The Byzantine victory at Nineveh led to a peace treaty in 628 which restored the old territorial boundaries, freed the Byzantines of tribute payments to Persia, and also led to the Sassanids returning the "True Cross" relic to the Byzantines. However, the war had exhausted both major empires and enabed the Arab Rashidun Caliphate to overwhelm both Byzantium and Persia in the coming decades.
Background[]
The Roman state was almost constantly at war with the Iranian empires since the 60s BC, with the first several wars being fought between the Roman Republic (the Roman Empire from 27 BC) against the Parthians, and later between the Eastern Roman Empire (the Byzantine Empire from 476 AD) and the Persian Sassanids. In the 3rd century AD, the Arab Ghassanids and Lakhmids migrated north from Yemen and became the vassal states of Eastern Rome and the Sassanids, respectively, serving as scouts, raiders, or light cavalry for both empires and staving off Arab tribal raids from the south. Both kingdoms' populations worshipped traditional Arab paganism and Monophysite Christianity; the Sassanids worried that the Arab Christians might harbor Roman sympathies, while the Orthodox Byzantines considered Monophysitism to be heretical. The Roman attempts to suppress the Monophysite heresy led to the Ghassanids rebelling against their overlordship from the late 6th to early 7th century, weakening Roman support in Arabia. On the other hands, religious tensions between the Lakhmids and Sassanids and Shah Khosrau II's attempts to implement direct rule in Arabia led to war. In 602, Khosrau deposed and executed the Lakhmid king al-Nu'man III and installed an Arab governor, Iyas ibn Qabisah al-Ta'i, in his place. The northern Arab tribes, led by Hantala bin Tha'laba al-Ajli, rebelled against the Sassanids, defeating them at the Battle of Dhi Qar in 609, but failing to end Sassanid rule in al-Hirah. This sequence of events created divided loyalties among the region's Arab tribes and stripped the Sassanid border of its traditional buffer.
War[]
In 602 AD, the Sassanids used the internal strife within Byzantium which followed the murder of Khosrau II's ally Maurice of Byzantium as a pretext to declare war, conquering much of the Levant, Egypt, several islands in the Aegean Sea, and parts of Anatolia. Although the Roman noble Heraclius took the throne in 611 and started to stabilize the situation, he failed to slow the enemy completely, as he was also caught up in a war with the Avars. Heraclius was able to gain momentum by winning two battles against the Sassanids from 622 to 625, and Khosrau responded by enlisting all men capable of fighting and turning the tide again. In 626, Shahbaraz, the Avars, and Sclaveni besieged Constantinople, but its defenders persevered, and, in 627, Heraclius allied with the Western Turkic Khaganate and invaded the Iranian heartland. He defeated the Sassanids at Nineveh in 627 and threatened Ctesiphon in 628, leading to the Persian nobles overthrowing Khosrau. His son Kavadh II became the next Shah, signing a peace treaty with Heraclius and paying a war indemnity; otherwise, the conflict achieved nothing apart from the restoration of the prewar borders.