For two hundred years after the death of Asparukh, in 661, the Bulgars were perpetually fighting either against the Greeks or else amongst themselves. At times a diversion was caused by the Bulgars taking the part of the Greeks, as in 718, when they ‘delivered’ Constantinople, at the invocation of the Emperor Leo, from the Arabs, who were besieging it. From about this time the Bulgarian monarchy, which had been hereditary, became elective, and the anarchy of the many, which the Bulgars found when they arrived, and which their first few autocratic rulers had been able to control, was replaced by an anarchy of the few. Prince succeeded prince, war followed war, at the will of the feudal nobles. This internal strife was naturally profitable to the Greeks, who lavishly subsidized the rival factions. At the end of the eighth century the Bulgars south of the Danube joined forces with those to the north in the efforts of the latter against the Avars, who, beaten by Charlemagne, were again pressing south-eastwards towards the Danube. In this the Bulgars were completely successful under the leadership of one Krum, whom, in the elation of victory, they promptly elected to the throne. Krum was a far more capable ruler than they had bargained for, and he not only united all the Bulgars north and south of the Danube into one dominion, but also forcibly repressed the whims of the nobles and re-established the autocracy and the hereditary monarchy. Having finished with his enemies in the north, he turned his attention to the Greeks, with no less success. In 809 he captured from them the important city of Sofia (the Roman Sardica, known to the Slavs as Sredets), which is to-day the capital of Bulgaria. The loss of this city was a blow to the Greeks, because it was a great centre of commerce and also the point at which the commercial and strategic highways of the peninsula met and crossed. The Emperor Nikiphóros, who wished to take his revenge and recover his lost property, was totally defeated by the Bulgars and lost his life in the Balkan passes in 811. After further victories, at Mesembria (the modern Misivria) in 812 and Adrianople in 813, Krum appeared before the capital, where he nearly lost his life in an ambush while negotiating for peace. During preparations for a final assault on Constantinople he died suddenly in 815. Though Krum cannot be said to have introduced civilisation into Bulgaria, he at any rate increased its power and gave it some of the more essential organs of government. He framed a code of laws remarkable for their rigour, which was undoubtedly necessary in such a community and beneficial in its effect. He repressed civil strife, and by this means made possible the reawakening of commerce and agriculture. His successor, of uncertain identity, founded in 822 the city of Preslav (known to the Russians as Pereyaslav), situated in eastern Bulgaria, between Varna and Silistria, which was the capital until 972.