But 626 was the decisive year of the war. The obstinate Chosroës determined on one final effort to crush Heraclius, by concerting a joint plan of operations with the Chagan of the Avars. While the main Persian army watched the emperor in Armenia, a great body under Shahrbarz slipped south of him into Asia Minor and marched on the Bosphorus. At the same moment the Chagan of the Avars, with the whole force of his tribe and of his Slavonic dependants, burst over the Balkans and beset Constantinople on the European side. The two barbarian hosts could see each other across the water, and even contrived to exchange messages, but the Roman fleet sailing incessantly up and down the strait kept them from joining forces. In the June, July, and August of 626 the capital was thus beset: the danger appeared imminent, and the Emperor was far away on the Euphrates. But the garrison was strong, the patrician Bonus, its commander, was an able officer, the fleet was efficient, and the same crusading fervour which had inspired the Constantinopolitans in 622 still buoyed up their spirits. In the end of July 80,000 Avars and Slavs, with all sorts of siege implements, delivered simultaneous assaults along the land front of the city, but they were beaten back with great slaughter. Next the Chagan built himself rafts and tried to bring the Persians across, but the Roman galleys sunk the clumsy structures, and slew thousands of the Slavs who had come off in small boats to attack the fleet. Then the Chagan gave up the siege in disgust and retired across the Danube. Heraclius had shown great confidence in the strength of Constantinople and the courage of its defenders. He sent a few veteran troops to aid the garrison, but did not slacken from his attack on Persia. While Shahrbarz and the Chagan were besieging his capital, he himself was wasting Media and Mesopotamia. He imitated King Chosroës in calling in Tartar allies from the north, and revenged the ravages of the Avars in Thrace by turning 40,000 Khazar horsemen loose on Northern Persia. The enemy gave way before him everywhere, and the Persians began to grow desperate. Next year King Chosroës put into the field the last levy of Persia, under a general named Rhazates, whom he bid to go out and “conquer or die.” At the same time he wrote to command Shahrbarz to evacuate Chalcedon and return home in haste. But Heraclius intercepted the despatch of recall, and Shahrbarz came not. Near Nineveh Heraclius fell in with the Persian home army and inflicted on it a decisive defeat. He himself, charging at the head of his cavalry, rode down the general of the enemy and slew him with his lance. Chosroës could put no new army in the field, and by Christmas Heraclius had seized his palace of Dastagerd, and divided among his troops such a plunder as had never been seen since Alexander the Great captured Susa.