all of Kievan Rus' until 1036. Like Vladimir, Yaroslav was eager to improve relations with the rest of Europe, especially the Byzantine Empire. Yaroslav's granddaughter, Eupraxia, the daughter of his son Vsevolod I, Prince of Kiev, was married to Henry IV, Holy Roman Emperor. Yaroslav also arranged marriages for his sister and three daughters to the kings of Poland, France, Hungary and Norway. Yaroslav promulgated the first East Slavic law code, Russkaya Pravda; built Saint Sophia Cathedral in Kiev and Saint Sophia Cathedral in Novgorod; patronized local clergy and monasticism; and is said to have founded a school system. Yaroslav's sons developed the great Kiev Pechersk Lavra (monastery), which functioned in Kievan Rus' as an ecclesiastical academy. Succession issues In the centuries that followed the state's foundation, Rurik's descendants shared power over Kievan Rus'. The means by which royal power was transferred from one Rurikid ruler to the next is unclear, however, with Magocsi (2010) saying: 'Scholars have debated what the actual system of succession was or whether there was any system at all.' According to Kollmann (1990), the rota system was used with the princely succession moving from elder to younger brother and from uncle to nephew, as well as from father to son. Junior members of the dynasty usually began their official careers as rulers of a minor district, progressed to more lucrative principalities, and then competed for the coveted throne of Kiev. Whatever the case, according to Katchanovski et al. (2013), 'no adequate system of succession to the Kyivan throne was developed' after the death of Yaroslav the Wise (), commencing a process of gradual disintegration. The unconventional power succession system fomented constant hatred and rivalry within the royal family. Familicide was frequently deployed to obtain power and can be traced particularly during the time of the Yaroslavichi (sons of Yaroslav), when the established system was skipped in the establishment of Vladimir II Monomakh as the Grand Prince of Kiev, in turn creating major squabbles between Olegovichi from Chernigov, Monomakhs from Pereyaslav, Izyaslavichi from Turov/Volhynia, and Polotsk Princes. The position of the Grand Prince of Kiev was weakened by the growing influence of regional clans. Fragmentation and decline The rival Principality of Polotsk was contesting the power of the Grand Prince by occupying Novgorod, while Rostislav Vladimirovich was fighting for the Black Sea port of Tmutarakan belonging to Chernigov. Three of Yaroslav's sons that first allied together