The Byzantine–Sasanian War of 602–628 was the final and most devastating of the series of wars fought between the Byzantine Empire and the Sasanian Empire of Iran. The previous war between the two powers had ended in 591 after Emperor Maurice helped the Sasanian king Khosrow II regain his throne. In 602 Maurice was murdered by his political rival Phocas. Khosrow proceeded to declare war, ostensibly to avenge the death of the deposed emperor Maurice. This became a decades-long conflict, the longest war in the series, and was fought throughout the Middle East: in Egypt, the Levant, Mesopotamia, the Caucasus, Anatolia, Armenia, the Aegean Sea and before the walls of Constantinople itself.