In archaeology, earthwork is a general term to describe artificial changes in land level. Typically, they are piles of artificially placed or sculpted rocks and soil. Earthworks are often known as barrows in England, and mounds in North America. Earthworks can themselves be archaeological features or they can show features beneath the surface.
Types of earthwork
Earthworks of interest to archaeologists include hillforts, henges, mounds, platform mounds, effigy mounds, enclosures, long barrows, tumuli, ridge and furrow, mottes, round barrows and other tombs.
- Hillforts, a type of fort made out of mostly earth and other natural materials including sand, straw, and water were built as early as the late Stone Age and were built more frequently during the Bronze Age as a means of protection 
- Henge earthworks are those that consist of a flat area of earth in a circular shape that are encircled by a ditch, or several circular ditches, with a bank on the outside of the ditch built with the earth from inside the ditch; they are believed to have been used as monuments for spiritual ritual ceremonies 
- A mound is a substantial manmade pile of earth or rocks that was frequently created to mark burial sites 
- Platform mounds are pyramid or rectangular-shaped mounds that are used to hold a building or temple on top.
- An effigy mound is a pile of earth, often very large in scale, that is shaped into the image of a person or animal, often for symbolic or spiritual reasons 
- An enclosure is a space that is surrounded by an earthwork.
- Long barrows are oblong-shaped mounds that are used for burials.
- A cross dyke or cross-ridge dyke is a bank and ditch, or sometimes a ditch between two banks, that crosses a ridge or spur of high ground. Found in Europe and often belonging to the later Bronze Age or Iron Age. Often marked on Ordnance Survey maps in the UK.
- Ridge and furrows are sets of parallel depressions and ridges in the ground formed primarily through historic farming techniques.
- Mottes are mound structures made of earth and stone that once held castles. They are an important part of the motte and bailey castle, a castle design during early Norman times in which the castle is built on the motte, and surrounded by a ditch and a bailey, which is an enclosure with a stone wall.
- A round barrow is a mound that is in a rounded shape that was used during Neolithic times as a burial mound.
Size of earthworks
Earthworks can vary in height from a few centimetres to the size of Silbury Hill at 40 metres (130 ft). They can date from the Neolithic to the present. The structures can also stretch for many tens of kilometres (e.g. Offa's Dyke and Antonine Wall). In area, they can cover many hectares; for example, Maiden Castle, which is 19 hectares (47 acres).
Shallow earthworks are often more visible as cropmarks or in aerial photographs if taken when the sun is low in the sky and shadows are more pronounced. Similarly, earthworks may be more visible after a frost or a light dusting of snow.
Earthworks can be detected an plotted using Light Detection And Ranging (LIDAR). This technique is particularly useful for mapping small variations in land height that would be difficult to detect by eye. It can be used to map features beneath forest canopy and for features hidden by other vegetation. LIDAR results can be input into a Geographic Information System (GIS) which can then produce three dimensional representations of the earthworks.
An accurate survey of the earthworks can enable them to be interpreted without the need for excavation. For example, earthworks from deserted medieval villages can be used to determine the location, size, and layout of lost settlements. Often these earthworks can point to the purpose of such a settlement, as well the context in which it existed.
North American Earthworks
Earthworks in North America consist of mounds built by Native Americans known as the Mound Builders. Ancient people who lived in the American Midwest commonly built effigy mounds, which are mounds shaped like animals (real or imaginary) or people. Possibly the most famous of these effigy mounds is Serpent Mound. Located in the Ohio, this 411 meter long earthen work is thought to memorialize alignments of the planets and stars that were of special significance to the Native Americans that constructed it. Cone-shaped or conical mounds are also numerous, with thousands of them scattered across the American Midwest, some over 80 feet tall. These conical mounds appear to be marking the graves of one person or even dozens of people. An example of a conical mound is the Miamisburg Mound located in central Ohio which has been estimated to have been built by people of the Adena culture in the time range of 800 B.C. to 100 AD. The American Plains also hold temple mounds, or platform mounds, which are giant pyramid-shaped mounds with flat tops that once held temples made of wood. An example of a temple mound is Monks Mound located at the Cahokia site in Collinsville Illinois.
During the American Civil War, earthwork fortifications were built throughout the country, by both Confederate and Union sides. The largest earthwork fort built during the war was Fortress Rosecrans, which originally encompassed 255 acres (103.2 ha).
- Muir, 77
- Wood, 85–96; see also: excavation
- Scott, Willie. "How Earthwork Forts were Built". Retrieved 13 April 2012.
- "The Definition of a Henge". Retrieved 13 April 2012.
- "Mound". Retrieved 13 April 2012.
- "Platform Mound". Retrieved 13 April 2012.
- "Effigy Mound". Retrieved 13 April 2012.
- "Enclosure". Retrieved 13 April 2012.
- "West Kennet Long Barrow". Retrieved 13 April 2012.
- "Tumulus". Retrieved 13 April 2012.
- Darvill, Timothy (2008). Oxford Concise Dictionary of Archaeology, 2nd ed., Oxford University Press, Oxford and New York, p. 116. ISBN 978-0-19-953404-3.
- Ordnance Survey 1:50,000 Landranger series.
- "Ridge and Furrow". Retrieved 13 April 2012.
- "Motte". Retrieved 13 April 2012.
- "Round Barrow". Retrieved 13 April 2012.
- Wilson, 38
- Aston, 14
- EID; crater beneath canopy
- Taylor, 59–60
- Feder, 54
- Crystal, Ellie. "Mounds of North America". Retrieved 4/12/12.
- Earl J. Hess (2005). "Field Armies and Fortifications in the Civil War". UNC Press. Retrieved May 20, 2013.
- Ed Bearss (1960). "Fortress Rosecrans Research Report". National Parks Service. Retrieved May 17, 2013.
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