This lecture is devoted to a most significant phenomenon in the history of Russian architecture, the three churches sharing the same name of Saint Sophia. These three churches, in Kiev, Novgorod, and Polotsk, are studied from different points of view (i.e. stylistic, artistic, engineering, and town-forming) and we come to a conclusion that these buildings have much more in common than just the name. The original Byzantine traditions adopted by the Russian culture evolved into something genuinely Russian.