and ended with the victory of his brother, Yaroslav the Wise in 1019. The Byzantine chronicler John Skylitzes writes of one "Sphengos, the brother of Vladimir" who assisted the imperial fleet in attacking "Khazaria" in 1016. According to the historians Simon Franklin and Jonathan Shepard, this Sphengoswhose name seems to be the Greek variant of the Varangian Svein or Sveinki namescould well have been identical with Mstislav. In 1022, Mstislav killed Rededia, the prince of the Circassian tribe of the Kassogians in a duel after violating the agreed upon rules in the duel. Rededia proposed a physical duel without the use of arms in order to spare the possibility of more war and death for the Kassogians who were already in a semi-permanent state of war. Mstislav agreed and the duel began: Rededia immediately asserted his dominance and defeated Mstislav. Caught unaware, Mstislav unsheathed a concealed dagger and betrayed Rededia and the honour of the duel by stabbing him. Rededia later, in his dying breaths, insisted that his comrades not hold a blood vendetta to avoid further gruelling wars for the Kassogians who had already fought the Mongols previous to Mstislav's campaign. Rededia's legacy was immortalized by his fellow Kassogian bards and his name continues to live even in modern Circassian minstrels, poems and folk songs. According to the Primary Chronicle, he seized Rededia's "wife and children" and "imposed tribute upon the Kasogians" after his victory. Many Kassogians joined Mstislav's druzhina or retinue. He had a church, dedicated to the Holy Virgin, built in his seat in fulfillment of the oath he had taken before the duel. Prince of Chernigov In 1024, while Yaroslav the Wise was away from Kiev, Mstislav led his army, which included Kassogian and Khazar troops, against the city. Although he could not enter the capital of Rus' because of the locals' opposition, he forced the Severiansan East Slavic tribe dwelling along the Desna River to the east of Kievto accept his suzerainty. He transferred his seat from Tmutarakan to Chernihiv, which was the second largest town in Kievan Rus'. For no source mentions a local prince ruling in Chernigov before this event, historians regard Mstislav as the first ruler of the Principality of Chernigov. He had the citadel expanded and the defensive works surrounding the suburb reinforced in his new seat. Duumvirate Yaroslav the Wise, who mustered Varangian troops in Novgorod, invaded Mstislav's domain in