Russia, or the Russian Federation, is a country in Eastern Europe and North Asia. It is the largest country in the world, spanning eleven time zones and sharing land borders with fourteen countries. With a population of over 140 million, Russia is the most populous country in Europe and the ninth-most populous in the world. It is a highly urbanised country, with sixteen of its urban areas having more than 1 million inhabitants. Moscow, the most populous metropolitan area in Europe, is the capital and largest city of Russia, while Saint Petersburg is its second-largest city and a major cultural centre. Human settlement on the territory of modern Russia dates back to the Lower Paleolithic. The East Slavs emerged in Europe between the 3rd and 8th centuries AD. The first East Slavic state, Kievan Rus', arose in the 9th century, and in 988 adopted Orthodox Christianity from the Byzantine Empire. The latter ultimately disintegrated, and the Grand Duchy of Moscow led the unification of Russian lands in the late 13th century, leading to the proclamation of the Tsardom of Russia in 1547. By the early 18th century, Russia had expanded vastly through conquest, annexation, and the efforts of Russian explorers, developing into the Russian Empire, the third-largest in history. The Russian Revolution of 1917 led to the monarchic system being abolished and replaced by the Russian Socialist Federative Soviet Republic, the first constitutionally socialist state in the world.