Mountains are areas of land with steep sides that rise sharply from surrounding land.  They can be found all around the world, with 20% of the Earth's surface being mountainous.  Mountains present both positive and negative aspects to human existence.  In the positive, mountains often act as barriers to invasion.  India, protected by the Himalaya Mountains, has enjoyed protection from invasion from other parts of Asia.  However, the barrier effect can also have negative effects.  cultural diffusion is often hampered as trade and other peaceful contact cannot occur.

Mountains also usually lack arable farm land.  This has often resulted in sparse human habitation.  But, in some places human adaptation to this geographical feature has allowed civilization to flourish.  In both China and Mesoamerica (Inca), terraces or steps, were cut into the mountain providing an area of flat land suitable for crops.  This is known as terrace farming.

In Greece, the mountainous terrain prevented the development of a unified society.  As a result, the Greeks formed city-states with a variety of government systems, including the first democracy. Another result of the mountainous terrain of Greece was the reliance on the sea as a source of food, and later trade.