In a range of hills, or especially of mountains, a pass (also gap, notch, col, saddle, bwlch, brennig or bealach) is a saddle point in between two areas of higher elevation.If following the lowest possible route through a range, a pass is locally the highest point on that route. Since many of the world's mountain ranges have always presented formidable barriers to travel, passes have been important since before recorded history, and have played a key role in trade, war and migration.
Topographically, a pass has the general form of a saddle between two mountains. They are often found just above the source of a river, constituting a sort of "bridge" over to the headwaters of a different river. Passes may be very short, consisting of steep slopes to the top of the pass, or valleys of many kilometers, whose highest point is only identifiable by surveying.
Roads have long been built through passes, and more recently railways. Some high and rugged passes may have tunnels bored underneath, so as to allow faster traffic flow all year.
The top of a pass is frequently the only flat ground in the area, a high vantage point, so it is often a preferred site for buildings. For countries whose borders are delimited by a mountain range, the pass is typically part of the border, and the facilities likely include a border control or customs station, and possibly a military post as well, as relatively few soldiers are required to guard a pass.. For passes with roads, it is also customary to have a small roadside sign giving the name of the pass and its elevation above mean sea level.
As well as offering relatively easy travel between valleys, passes also provide a route between two mountain tops with a minimum of descent. As a result, it is common for tracks to meet at a pass; this often makes them convenient routes even when travelling between a summit and the valley floor.
There are thousands of named passes around the world, some of which are well-known, such as the Great St. Bernard Pass at 2,473 metres (8,110 ft) in the Alps, the Khyber Pass at 1,027 metres (3,370 ft) between Afghanistan and Pakistan, and the Khardung La at 5,359 metres (17,580 ft) in Jammu and Kashmir, India. The Marsimik La at 5,590 metres (18,300 ft) is a lesser-known pass; it is one of the world's highest motorable passes and lies in India, on the northern-most tip of the Changthang Plateau, near the Chinese border.
There are many words for pass in the English-speaking world. In the United States, the southern Appalachians more commonly use the word gap, and notch is often heard in New England. Scotland has the Gaelic term bealach (anglicised "Balloch"). In the Lake District of north west England, the term hause is often used, although the term pass is also common — one distinction is that a pass can refer to a route, as well as the highest part thereof, while a hause is simply that highest part, often flattened somewhat into a high level plateau.
