"double faith", the coexistence and mutual penetration of two religions—the "popular" and the "official". Popular culture has long been defined by pagan beliefs, especially in the remote regions of Kievan Rus’. Subsequently, it was defined by a simplified interpretation of Christianity and by superstitions, similar to what had happened in Western European culture. However, Russian historians’ idea of the popular culture after Christianization is primarily based on indirect data and suppositions. At the same time, the culture of the ecclesiastical and secular elite is known for its monuments, which do not allow historians to make confident conclusions on pagan penetration of religious beliefs of Medieval Rus’. Historians prefer to speak of a parallel development of popular and "elitist" cultures. They certainly give credit to the earlier traditions of the Early East Slavs and Finnic peoples without, however, overestimating their significance in forming elements of the culture. With the adoption of Christianity, the principalities of Rus’ became part of a book culture. Although written language had been in use in the Russian lands for quite some time, it was only after the baptism of Rus’ that written language spread throughout the principalities. The development of the local literary language was associated with Christianity, and strongly influenced by Old Church Slavonic. An abundance of translated literature laid the foundation for the development of Russia's own writing traditions. At its early stages, the most typical genres were sermons, lives of the saints (for example, Life of Boris and Gleb), descriptions of military campaigns (the famous Tale of Igor's Campaign), and composition of chronicles (Primary Chronicle). Suzdalian period As part of the Christian world, Rus principalities gained a wide range of opportunities for developing their political and cultural ties not only with Byzantium, but with the European countries, as well. By the end of the eleventh century, Rus gradually fell under the influence of Roman architecture. Whitestone cathedrals, decorated with sculpture, appeared in the principality of Vladimir-Suzdal due to Andrei Bogolyubsky's invitation of architects from "all over the world". According to Russian historian Vasili Tatischev, the architects were sent to Vladimir by the Holy Roman Emperor Frederick Barbarossa. These cathedrals, however, are not identical with the Roman edifices of Catholic Europe and represent a synthesis of the Byzantine cruciform plan and cupolas with Roman whitestone construction and decorative technique. This mixture of Greek and Western European traditions was possible only in Russia. One of