Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. Europe is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, and the Mediterranean Sea to the south. It comprises the westernmost part of Eurasia. Europe is generally considered as separated from Asia by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways of the Turkish Straits. Yet the non-oceanic borders of Europe—a concept dating back to classical antiquity—are arbitrary and amount to a historical and social construct. The primarily physiographic term "continent" as applied to Europe also incorporates cultural and political elements whose discontinuities are not always reflected by the continent's current overland boundary with Asia.