Heraclius (575-641) was son of Heraclius the Elder, exarch of Africa, who led a revolt against the usurper emperor Phocas, deposing him in 610. Heraclius became emperor and was immediately forced to deal with multiple threats on many frontiers. One of the main frontiers was the Byzantine-Sassanid War of 602-628 against King Khosrau II and the Sassanid Empire. The Sassanids managed to fight all the way to the walls of Constantinople before failing to penetrate them, allowing Heraclius to counter-attack and drive them all the way back to the capital of Ctesiphon. Khosrau was executed by his son Kavadh II, and a peace treaty was agreed to. The Sassanid Empire soon fell to the Muslim conquests, another threat Heraclius had to deal with. Heraclius was credited for making Greek the Byzantine Empire's official language, as well as for his enlarging of the empire and his reorganisation of government and military. Though his attempts at religious harmony failed, he was successful in returning t