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. Phocas' brutal repression sparked a succession crisis that ensued as the general Heraclius sent his nephew Nicetas to attack Egypt, enabling his son Heraclius the younger to claim the throne in 610. Phocas, an unpopular ruler who is invariably described in Byzantine sources as a "tyrant", was eventually deposed by Heraclius, having sailed from Carthage. Around the same time, the Persians completed their conquest of Mesopotamia and the Caucasus, and in 611 they overran Syria and entered Anatolia, occupying Caesarea. Having expelled the Persians from Anatolia in 612, Heraclius launched a major counter-offensive in Syria in 613. He was decisively defeated outside Antioch by Shahrbaraz and Shahin, and the Roman position collapsed. Over the following decade the Persians were able to conquer Palestine, Egypt, Rhodes and several other islands in the eastern Aegean, as well as to devastate Anatolia. Meanwhile, the Avars and Slavs took advantage of the situation to overrun the Balkans, bringing the Roman Empire to the brink of destruction. During these years, Heraclius strove to rebuild his army, slashing non-military expenditures, devaluing the currency and melting down Church plate, with the backing of Patriarch Sergius, to raise the necessary funds to continue the war. In 622, Heraclius left Constantinople, entrusting the city to Sergius and general Bonus as regents of his son. He assembled his forces in Asia Minor and, after conducting exercises to revive their morale, he launched a new counter-offensive, which took on the character of a