of his daughter Rogneda (Norse: Ragnhild). The high-born princess refused to affiance herself to the son of a bondswoman (and was betrothed to Yaropolk), so Vladimir attacked Polotsk, took Ragnhild by force, and put her parents to the sword. Polotsk was a key fortress on the way to Kiev, and capturing Polotsk and Smolensk facilitated the taking of Kiev in 978, where he slew Yaropolk by treachery and was proclaimed knyaz of all Kievan Rus. Years of pagan rule Vladimir continued to expand his territories beyond his father's extensive domain. In 981, he seized the Cherven towns from the Poles; in 981–982, he suppressed a Vyatichi rebellion; in 983, he subdued the Yatvingians; in 984, he conquered the Radimichs; and in 985, he conducted a military campaign against the Volga Bulgars, planting numerous fortresses and colonies on his way. Although Christianity had spread in the region under Oleg's rule, Vladimir had remained a thoroughgoing pagan, taking eight hundred concubines (along with numerous wives) and erecting pagan statues and shrines to gods. He may have attempted to reform Slavic paganism in an attempt to identify himself with the various gods worshipped by his subjects. He built a pagan temple on a hill in Kiev dedicated to six gods: Perun—the god of thunder and war, a god favored by members of the prince’s druzhina (military retinue)"; Slav gods Stribog and Dazhd'bog; Mokosh—a goddess representing Mother Nature "worshipped by Finnish tribes"; Khors and Simargl, "both of which had Iranian origins, were included, probably to appeal to the Poliane." Open abuse of the deities that most people in Rus' revered triggered widespread indignation. A mob killed the Christian Fyodor and his son Ioann (later, after the overall Christianisation of Kievan Rus', people came to regard these two as the first Christian martyrs in Rus', and the Orthodox Church set a day to commemorate them, 25 July). Immediately after the murder of Fyodor and Ioann, early medieval Rus' saw persecutions against Christians, many of whom escaped or concealed their belief. However, Prince Vladimir mused over the incident long after, and not least for political considerations. According to the early Slavic chronicle, the Tale of Bygone Years, which describes life in Kievan Rus' up to the year 1110, he sent his envoys throughout the world to assess first-hand the major religions of the time: Islam, Roman Catholicism, Judaism, and Byzantine Orthodoxy. They were most impressed with