The Byzantine style of churches, which was imported from Kiev, was adapted to a distinctive Novgorodian style through the ecclesiastical constructions commissioned by the princes in the eleventh and twelfth centuries. Novgorod's medieval architecture owes its distinctive style to the adaptation of Byzantine and Kievan styles to its local conditions. As there was not a nearby source of surface stone and its brickmaking capabilities was limited in the area, construction of Novgorodian masonry churches were made using a method of masonry using rough-hewn local stone such as limestone with a crushed brick and lime cement, resulting in a pink surface similar to that used in contemporary Kievan churches but with a coarser surface texture. Unlike the cathedral in Kiev, the Novgorodian St Sophia only has five main domes rather than 13 like in Kiev (representing Christ and the twelve apostles). During the twelfth century, the central dome was redone externally to be converted into an onion dome. These onion domes are a distinct feature of Russian architecture. Most likely adopted for its aesthetic qualities, the unique shape of the domes also provide the advantage of preventing the accumulation of snow. While the churches constructed in the twelfth century didn’t rival the Cathedral of St Sophia in scale or complexity, the princes continued their show of power in their architectural projects. The Cathedral of St George of Yuriev Monastery was commissioned in 1119 by Prince Vsevolod of Pskov and is another example of one of these princely churches. The architect was known as Master Peter, one of the few architects who have been recorded at this time in Russia. The exterior is characterized by narrow windows and double-recessed niches, which proceed in a rhythm across the façade; the interior walls reach a height of . Its pillars are closely spaced, emphasizing the height of the vaulted ceilings. The interior was covered in frescoes from the prince’s workshops, including some of the rarest Russian paintings of the time. Three more churches show the style of the princely churches created during this time: the Cathedral of St Nicholas in Iaroslav Court (1113), the Church of the Nativity of the Virgin at Antoniev Monastery (1117-1119), and the Church of John the Baptist in Petriatin Courty (1127-30). Several characteristics are present in the churches, and they draw a more simplistic form of that of the Cathedral of St Sophia. After the Mongols invaded, Novgorod suffered