<P> A mountain pass is a navigable route through a mountain range or over a ridge . Since many of the world's mountain ranges have presented formidable barriers to travel, passes have played a key role in trade, war, and both human and animal migration throughout Earth's history . At lower elevations it may be called a hill pass . The highest vehicle - accessible pass in the world appears to be Mana Pass, located in the Himalayas on the border between India and Tibet, China . </P> <P> Mountain passes make use of a gap, saddle, or col (also sometimes a notch, the low point in a ridge). A topographic saddle is analogous to the mathematical concept of a saddle surface, with a saddle point marking the highest point between two valleys and the lowest point along a ridge . On a topographic map, passes are characterized by contour lines with an hourglass shape, which indicates a low spot between two higher points . </P> <P> Passes are often found just above the source of a river, constituting a drainage divide . A pass may be very short, consisting of steep slopes to the top of the pass, or may be a valley many kilometres long, whose highest point might only be identifiable by surveying . </P>

Why do you think are the passes in the mountains important