Shortly after their settlement the two younger brothers died and Rurik became sole chief of all the Varangian bands in northern Russia and assumed the title of grand-prince. He now became so powerful that he was able to subject Novgorod, which he made the capital of an empire stretching from the lakes in the north to the sources of the Dnieper in the south.[a] The country drained by that river was also occupied by Varangians, but independently of Rurik. Two chiefs by the name of Askold and Dir (Scand. Höskaldr and Dyri) wrested Kiev from the Chazars and ruled over the Polians, the most civilized tribe of the eastern Slavs. In 865 they led against Byzantium an expedition which consisted of at least two hundred ships, and according to Venetian accounts of three hundred and sixty ships, to which would correspond an army of about fourteen thousand warriors. A tempest arose and destroyed the fleet in the sea of Marmora. The barbarians attributed their disaster to the wonder-working virgin, and it is reported that Askold embraced Christianity. This expedition has a two-fold importance: (1) it gives us the _first_ certain date in Russian history; and (2) it introduced the seeds of Christianity into Russia. In the following year, 866, the patriarch Photius established a bishopric at Kiev. After the death of his brothers Rurik reigned till his death in 879, when he was succeeded, not by his son Igor (Scand. Ingvarr), but by the eldest member of his family Oleg (Scand. Helge). In 882 he set out from Novgorod with an army composed of Varangians and the subject Slavo-Finnish tribes--Tchuds, Merians, Vesians, Ilmen Slavs, and Krivitchi--sailed down the upper Dnieper, took Smolensk, freed the Radimichi and the Severians from the yoke of the Chazars and incorporated them in his empire, and finally reached Kiev. Askold and Dir were then got rid of by an act of treachery, and Kiev was made the capital of an empire embracing nearly all the eastern Slavs. _The Treaty with Constantinople_ But Kiev was only one of the stages in the southward progress of the Varangians. The great city of the east, Constantinople, was the glittering prize that dazzled their eyes and was ever regarded as the goal of their ambition. Accordingly, in 907, Oleg sailed with a fleet of two thousand boats and eighty thousand men, and reached the gates of Constantinople. The frightened emperor was obliged to pay a large ransom for the city and to agree to a treaty of free commercial intercourse between the Russians and the Greeks. A particular district in the suburbs of the city was assigned as the place of residence for Russian traders, but the city itself could be visited by no more than fifty Russians simultaneously, who were to be unarmed and accompanied by an imperial officer.[g][a]