A hill is a landform that extends above the surrounding terrain. It often has a distinct summit, and is usually applied to peaks which are above elevation compared to the relative landmass, though not as prominent as mountains.
Terminology
The distinction between a hill and a mountain is unclear and largely subjective, but a hill is universally considered to be not as tall, or as steep as a mountain.
Geographers historically regarded mountains as hills greater than above sea level, which formed the basis of the plot of the 1995 film The Englishman who Went up a Hill but Came down a Mountain. In contrast, hillwalkers have tended to regard mountains as peaks above sea level. The Oxford English Dictionary also suggests a limit of and Whittow states "Some authorities regard eminences above as mountains, those below being referred to as hills." Today, a mountain is usually defined in the UK and Ireland as any summit at least high, while the official UK government's definition of a mountain is a summit of or higher. Some definitions include a topographical prominence requirement, typically or . In practice, mountains in Scotland are frequently referred to as "hills" no matter what their height, as reflected in names such as the Cuillin Hills and the Torridon Hills. In Wales, the distinction is more a term of land use and appearance and has nothing to do with height.
For a while, the US defined a mountain as being or more tall. Any similar landform lower than this height was considered a hill. The United States Geological Survey, however, has concluded that these terms do not in fact have technical definitions in the US
The Great Soviet Encyclopedia defined "hill" as an upland with a relative height of up to .
A hillock is a small hill. Other words include knoll and (in Scotland, Northern Ireland and northern England) its variant, knowe. Artificial hills may be referred to by a variety of technical names, including mound and tumulus.
Hills may form through geomorphic phenomena: faulting, erosion of larger landforms such as mountains and movement and deposition of sediment by glaciers (notably moraines and drumlins or by erosion exposing solid rock which then weathers down into a hill). The rounded peaks of hills results from the diffusive movement of soil and regolith covering the hill, a process known as downhill creep.
Various names may be used to describe types of hills, based on appearance and method of formation. Many such names originated in one geographical region to describe a type of hill formation particular to that region, though the names are often adopted by geologists and used in a wider geographical context. These include:
Brae – Scots, Ulster, and North of England term for a hillside or brow of a hill. Drumlin – an elongated whale-shaped hill formed by glacial action. Butte – an isolated hill with steep sides and a small flat top, formed by weathering. Kuppe – a rounded hill or low mountain, typical of Central Europe. Tor – a rock formation found on a hilltop; also used to refer to the hill, especially in South West England and the Peak District. Puy – used especially in the Auvergne, France, to describe a conical volcanic hill. Pingo – a mound of earth-covered ice found in the Arctic and Antarctica.
Historical significance
Many settlements were originally built on hills, either to avoid floods (particularly if they were near a large body of water), for defense (since they offer a good view of the surrounding land and require would-be attackers to fight uphill), or to avoid densely forested areas. For example, Ancient Rome was built on seven hills, helping to protect it from invaders.
Some settlements, particularly in the Middle East, are located on artificial hills consisting of debris (particularly mudbricks) that has accumulated over many generations. Such a location is known as a "tell".
In Northern Europe, many ancient monuments are sited in heaps. Some of these are defensive structures (such as the hillforts of the Iron Age), but others appear to have hardly any significance. In Britain, many churches at the tops of hills are thought to have been built on the sites of earlier pagan holy places. The Washington National Cathedral in Washington, D.C. has followed this tradition and was built on the highest hill in that city.
Some cities' hills are culturally significant in their foundation, defense, and history. In addition to Rome, hills have played a prominent role in the history of San Francisco, with its hills being central to the city's fog and civil engineering projects today famous as tourist attractions such as the cable cars and Lombard Street.