The capital and largest city of Russia, in the western part of the country on the Moscow River, flowing about 500 km (310 mi) eastward to the Oka River. First mentioned in 1147, Moscow became the capital of the principality of Muscovy and by the 1400s was the capital of the Russian state and the seat of the metropolitan (later patriarch) of the Russian Orthodox Church. The capital was transferred to St. Petersburg in 1712 but was returned to Moscow by the Soviets in 1918.