The four geographical boundaries that divide Europe from Asia are the Bosphorus, the Dardanelles, the Caucasus and the Ural Mountains. Together, these four boundaries create a geographical line that stretches extends north to south through the western quarter of Russia, goes around the western boarder of Kazakhstan and the Caspian Sea, and runs east to west along the northern border of Turkey and Azerbaijan.
The Bosphorus is a narrow straight that connects the Black Sea with the Sea of Marmara, and the Dardanelles is another narrow strait on the south side of the Sea of Mamara that connects it to the Aegean Sea. The Caucasus is a narrow bridge of land between the Caspian and Black Seas that includes many small republics with close ties to Russia, including Azerbaijan and Georgia. Finally, the Ural Mountains are a long mountain range in Russia that stretch from the Arctic Ocean in the north to the Ural River in the south.
Russia lies on both sides of the Europe/Asia line. Siberia and the majority of the country's land is in Asia, while the largest cities in Russia are located in the western part of the country and therefore considered to be geographically in Europe.