Toward the beginning of his reign, Khosrow II had good relations with the Byzantines. However, when in 602 Emperor Maurice was murdered by his General Phocas (602–610), who usurped the Roman (Byzantine) throne, Khosrow launched an offensive against Constantinople: ostensibly to avenge Maurice's death, but his aim clearly included the annexation of as much Byzantine territory as was feasible. Khosrow II, along with Shahrbaraz and his other best generals, quickly captured Dara and Edessa in 604, and recaptured lost territory in the north, which made the Sasanian–Byzantine borders go back to the pre-591 frontier before Khosrow gave Maurice territory in return for military aid against Bahram Chobin. After having reclaimed lost territory, Khosrow withdrew from the battlefield and handed military operations to Shahrbaraz and Shahin Vahmanzadegan. The Sasanian armies then invaded and plundered Syria and Asia Minor, and in 608 advanced into Chalcedon.