The architecture of Kievan Rus' comes from the medieval state of Kievan Rus' which incorporated parts of what is now modern Ukraine, Russia, and Belarus, and was centered on Kiev and Novgorod. Its architecture is the earliest period of Russian architecture, using the foundations of Byzantine culture but with great use of innovations and architectural features. Most remains are Russian Orthodox churches or parts of the gates and fortifications of cities. After the disintegration of Kievan Rus' followed by Mongol invasion in the first half of the 13th century, the architectural tradition continued in the principalities of Novgorod, Vladimir-Suzdal, Galicia-Volhynia and eventually had direct influence on the Russian, Ukrainian, and Belarusian architecture. The Old Russian architecture of churches originates from the pre-Christian Slavic "zodching" ( - construction). Church architecture The great churches of Kievan Rus', built after the adoption of Christianity in 988, were the first examples of monumental architecture in the East Slavic lands. The architectural style of the Kievan state, which quickly established itself, was strongly influenced by Byzantine architecture. Early Eastern Orthodox churches were mainly made of wood with the simplest form of church becoming known as a cell church. Major cathedrals often featured scores of small domes, which led some art historians to take this as an indication of what the pagan Slavic temples should have looked like. The 10th-century Church of the Tithes in Kiev was the first cult building to be made of stone. The earliest Kievan churches were built and decorated with frescoes and mosaics by Byzantine masters. Another great example of an early church of Kievan Rus' was the thirteen-domed Saint Sophia Cathedral in Kiev (1037–54), built by Yaroslav the Wise. Much of its exterior has been altered with time, extending over the area and eventually acquiring 25 domes. Saint Sophia Cathedral in Novgorod (1045–1050), on the other hand, expressed a new style that exerted a strong influence on Russian church architecture. Its austere thick walls, small narrow windows, and helmeted cupolas have much in common with the Romanesque architecture of Western Europe. Even further departure from Byzantine models is evident in succeeding cathedrals of Novgorod: St Nicholas's (1113), St Anthony's (1117–19), and St George's (1119). Along with cathedrals, of note was the architecture of monasteries of these times. The 12th–13th centuries were the period of feudal division of Kievan Rus into princedoms which were in nearly permanent feud, with multiplication of