Earthworks, also known as fieldworks or earthen fortifications, have been used throughout American military history as a form of defense. Many cultures, including those of Native Americans, have used forms of fortifications for thousands of years. However, the development of fortifications used in the United States during the eighteenth and nineteenth centuries, is European in origin.

The basic function of earthworks is relatively simple, to place a barrier between yourself and the enemy. Most earthen fortifications consist of two basic parts. The first part is a wall of earth, generally refered to as a parapet. Besides earth, a parapet could also contain wood or stone, which added strength and stability to the form. The second of these two basic parts is the ditch or trench. This provided the necessary soil for the parapet. If in front of the parapet it served as an additional obstacle for enemy troops; if placed behind the parapet it provided a protected avenue for troop movement. Many more featues could also be added to provide additional protection, to allow special placements for artillery, or to create additional obstacles for enemy troops.

Earthworks were constructed in a great variety of forms depending upon their functions. Provisional earthworks, constructed for long term occupation, can be highly engineered, complex geometric forms with several lines of defense. At the other end of the spectrum are hasty entrenchments. These can be a single line of works along the crest of a hill, or a rifle pit used by a single soldier.

There are three primary natural phenomena which contribute to the destruction of earthworks. These causes are the windthrow of large canopy trees, the colonization of earthworks by undesirable plant species, and the burrowing of animals.

The most dramatic of these natural processes is the windthrow of large canopy trees. If a blown-down tree was growing on an earthwork, its roots can tear away large quantities of soil and rock which make up the fortification. Trees growing near earthworks can also gouge out sections if they are blown-down and fall onto the structures. Both of these examples leave the soil exposed to the process of erosion.

A second natural phenomenon that diminishes the erosion-controlling capability of an herbaceous cover on earthworks is the colonization of undesirable plant species. Invasive woody plant species are considered undesirable if they do not provide good year-around erosion control or if they shade out more desirable grasses and forbs. Undesirable herbaceous plant species would include plants which have poor erosion control capabilities and which reduce plant diversity through aggressive competition. Management programs to inhibit the colonization and spread of invasive species are necessary in order to promote the highest degree of protection for earthworks from erosion.

The burrowing of animals in earthworks is the the third of the significant natural processes which damage earthworks. Groundhogs are the animal which most commonly cause this type of damage and have been observed in all types of sites. Although animals are generally left alone, if significant damage is being done to earthworks it may be necessary to remove them from the area.

Human impacts can also cause erosion on earthworks. Most deleterious human impacts can be grouped into two primary categories. These are inapropriate recreational activities and aggressive maintenance and management activities.

Because earthworks are typically higher than their surroundings, there is an attraction for visitors to walk on or over earthworks in battlefield parks. From this vantage point they can view the landscape and imagine the action of the battle. Unfortunately, this type of repeated trampling can cause extensive damage to earthworks. Further irreparable damage can be caused by riding mountain bikes, other recreational vehicles, and horses on earthworks. All these recreational activities are clearly in conflict with the goal of earthwork preservation.

Sometimes our own maintenance practices can be damaging to earthworks. Mowing is an activity with particularly high potential for causing damage to earthworks. Many units of the National Park Service use specialized mowing equipment to reduce potential impacts to the resources. Many units also reduce mowing frequency on earthworks to once a season.

Over the last decade, the National Park Service has made progress in developing a wholistic approach to earthworks planning and management. The 1989 Earthworks Landscape Management Manual was the first major step in this development. Drawing upon information gained since this first exploration, work began in 1995 on a refinement and expansion of the Manual. A 90% draft of this second work, the Guide to Sustainable Earthworks Management, is available for review in the Journals section of this site.

The National Park Service manages many battlefield units where earthworks exist. In the Mid-Atlantic States alone, there are hundreds of miles of earthworks, forts, and their associated features. The following parks in the Mid-Atlantic States have excellent examples of preserved earthworks from both the Revolutionary and Civil Wars.

• Colonial National Historical Park
• Fredericksburg & Spotsylvania National Military Park
• Gettysburg National Military Park
• Petersburg National Battlefield
• Richmond National Battlefield Park
• Valley Forge National Historical Park