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