Inarchaeology,earthworks are artificial changes in land level, typically made from piles of artificially placed or sculpted rocks and soil. Earthworks can themselves be archaeological features, or they can show features beneath the surface.[1]
There are two broad categories of archaeological earthwork: positive features where earth is built up above the previous ground level, and negative features which are cut into the landscape.[2] Beyond this, earthworks of interest to archaeologists includehill forts,henges,mounds,platform mounds,effigy mounds,enclosures,long barrows,tumuli,ridge and furrow,mottes,round barrows, and othertombs.[3]
Earthworks can vary in height, from a few centimetres to the size ofSilbury Hill at 40 metres (130 ft). They can date from theNeolithic to the present. The structures can also stretch for many tens of miles (e.g.Offa's Dyke andAntonine Wall). In area, they can cover many hectares; for example,Maiden Castle, which is 19 hectares (47 acres).
Shallow earthworks are often more visible ascropmarks or inaerial photographs if taken when the sun is low in the sky and shadows are more pronounced.[17] Similarly, earthworks may be more visible after a frost or a light dusting of snow.[18]
Earthworks can be detected and 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[19] and for features hidden by other vegetation. LIDAR results can be input into a geographic information system (GIS) to produce three-dimensional representations of the earthworks.
An accuratesurvey of the earthworks can enable them to be interpreted without the need forexcavation.[20] For example, earthworks fromdeserted 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.
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Earthworks in North America includemounds built by Native Americans known as theMound Builders. Ancient people who lived in the AmericanMidwest commonly builteffigy mounds, which are mounds shaped like animals (real or imaginary) or people. Possibly the most famous of these effigy mounds isSerpent Mound. Located inOhio, this 411-metre-long (1,348 ft) earthen work is thought to memorialize alignments of the planets and stars that were of special significance to theNative Americans that constructed it.[21] Cone-shaped orconical mounds are also numerous, with thousands of them scattered across the American Midwest, some over 24 m (80 ft) tall. These conical mounds appear to be marking the graves of one person or even dozens of people.[22] An example of a conical mound is theMiamisburg Mound in central Ohio, which has been estimated to have been built by people of theAdena culture in the time range of 800 BC to 100 AD.[23] The American Plains also hold temple mounds, orplatform mounds, which are giant pyramid-shaped mounds with flat tops that once held temples made of wood. Examples of temple mounds includeMonks Mound located at theCahokia site in Collinsville, Illinois,[22] and Mound H at theCrystal River site inCitrus County,Florida.[24] The earthworks atPoverty Point occupy one of the largest-area sites in North America, as they cover some 920 acres (320 ha) of land in Louisiana.[25]
Military earthworks can result in subsequent archaeological earthworks. Examples includeRoman marching forts, which can leave small earthworks. During theAmerican Civil War, earthwork fortifications were built throughout the country, by bothConfederate andUnion soldiers.[26] The largest earthwork fort built during the war wasFortress Rosecrans, which originally encompassed 255acres (103 ha).[27][relevant?]
In northeasternSomalia, near the city ofBosaso at the end of the Baladi valley, lies an earthwork 2 to 3 km (1.2 to 1.9 mi) long.[28][29] Local tradition recounts that the massive embankment marks the grave of a community matriarch. It is the largest such structure in the widerHorn region.[29]
Bigo bya Mugenyi is an extensive earthworks site in theinterlacustrine region of southwesternUganda. On the south shore of theKatonga river, the Bigo earthworks consist of a series of ditches and berms comprising an outer arch that encompasses four interconnected enclosures. When combined, the Bigo earthworks measure more than 10 km (6 mi) long.[30]Radiometric dates fromarchaeological investigations at Bigo date the earthworks to roughly AD 1300–1500, and they have been called Uganda's "largest and most important ancient monument".[31]
TheSteppe Geoglyphs, discovered in 2007 using Google Earth, are an example of earthworks in Central Asia.
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