In 602 the Roman army campaigning in the Balkans mutinied under the leadership of Phocas, who succeeded in seizing the throne and then killed Maurice and his family. Khosrau II used the murder of his benefactor as a pretext for war and reconquer the Roman province of Mesopotamia. In the early years of the war the Persians enjoyed overwhelming and unprecedented success. They were aided by Khosrau's use of a pretender claiming to be Maurice's son, and by the revolt against Phocas led by the Roman general Narses. In 603 Khosrau defeated and killed the Roman general Germanus in Mesopotamia and laid siege to Dara. Despite the arrival of Roman reinforcements from Europe, he won another victory in 604, while Dara fell after a nine-month siege. Over the following years the Persians gradually overcame the fortress cities of Mesopotamia by siege, one after another. At the same time they won a string of victories in Armenia and systematically subdued the Roman garrisons in the Caucasus.