Asia is the central and eastern part of Eurasia, comprising approximately fifty countries. It has an area, including islands, of roughly 49,694,700 km². Asia is joined to Africa by the Isthmus of Suez and to Europe by a long border generally following the Ural Mountains.
Asia is the largest and most populous region or continent, depending on the definition. It is traditionally defined as part of the landmass of Africa-Eurasia lying east of the Suez Canal, east of the Ural Mountains, and south of the Caucasus Mountains and the Caspian and Black Seas. About 60% of the world's human population lives in Asia.
Medieval Europeans considered Asia as a continent, a distinct landmass. The European concept of the three continents in the Old World goes back to classical antiquity with the etymology of the word rooted in the ancient Near and Middle East. The demarcation between Asia and Africa is the Isthmus of Suez and the Red Sea. The boundary between Asia and Europe is commonly believed to run through the Dardanelles, the Sea of Marmara, the Bosporus, the Black Sea, the Caucasus Mountains, the Caspian Sea, the Ural River to its source, and the Ural Mountains to the Kara Sea near Kara, Russia. However, modern discovery of the extent of Africa and Asia made this definition rather anachronistic, especially in the case of Asia, which would have several regions that would be considered distinct landmasses if these criteria were used (for example, South Asia and East Asia).
