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  1. Military Earthworks - Historical Overview

Original text by David Lowe and Paul Hawke,

edited for Currents by Lucy Lawliss
Fortification, or Military Architecture, is no other thing than an Art, which teaches Men to Fortifie themselves with Ramparts, Parapets, Moats, Covert Ways and Glacis, to the end the Enemy may not be able to attack such a part without great loss of his men; and that the small Number of Soldiers which defend the Place may be able to hold out for some time.

Sebastien le Prestre de Vauban (1633-1707)


Military earthworks have been with us since the first stirrings of organized warfare. The Roman legions, for example, were adept at defending themselves with earth and by habit entrenched their camps every night when marching through enemy territory. Soldiers have described military earthworks variously as entrenchments, fortifications, breastworks, fieldworks, or trenches. Engineers often used more technical terms for classic earthwork forms, such as redoubts, lunettes, bastions, ramparts, and redans. In its most basic structure, an earthwork is simply an excavation, composed of two elements—a protective mound of earth called a parapet, and the ditch from which the earth was removed. The ditch can be excavated in front of the parapet or behind it. The way these elements are combined and arranged on the ground results in a range of outward forms that vary according to terrain and the intended function of the structure. Construction is guided by an underlying military logic. As with any excavation, the volume of the parapet tends to be proportional to the depth and width of the ditch. Linear earthworks may vary in width from five to forty feet, and in length from a few feet to many miles. Often soldiers constructed auxiliary structures, such as military roads, batteries, dugouts, magazines, or foxholes, to expand a defensive position into a complex system of earthen fortifications. For purposes of cultural resource management, it is sufficient to define military earthworks as any earthen structure excavated for military purposes.

Soldiers build earthworks today as they did in ancient times—either to defend a fixed position, to enable a smaller number of defenders to resist a larger number of attackers, or to seal off an enemy town or strong point. Historically, soldiers or their laborers dug with shovels and picks, or burrowed frantically with bayonets and hands if in a desperate situation. While modern soldiers might resort to bulldozers and backhoes, the entrenching tool is still an essential part of the infantryman’s kit. Over time, the form and complexity of military earthworks have evolved in direct response to advances in weaponry, but today’s entrenchments owe much to their historic precedents. Although technologies have changed, the underlying military logic of defense has remained a constant over the centuries.
Until recently, few preservation efforts have sought to encompass entire earthworks systems. Military earthworks management has often been a low priority, and there have been differing approaches to treatment and management. Many earthworks have survived in woodlands by salutary neglect; others have been “opened up” by removing the trees, sometimes with the unintended consequence of erosion and resource degradation. Whether earthworks remain under tree cover or are provided with alternative protection, it is clear that resource managers must take a more active role in preserving these inherently fragile earthen structures for future generations. Active management requires familiarity with the purposes, types, modes of construction, and history of these resources. This section provides an introduction to the vocabulary, sources, and history of earthworks and to many of the characteristic forms that researchers and resource managers are likely to encounter in the field.

History of Earthworks Design and Construction

Native American peoples fortified their villages and towns for centuries before Europeans arrived, and examples of their earthen defenses follow the basic parapet and exterior ditch construction. The parapet was often topped by a log stockade that was impervious to arrows. Such defenses were effective in preventing surprise attacks by marauding war parties but provided less protection from firearms and cannon. Europeans imported not only new weaponry but also new forms of defense against those weapons and imposed their own concepts on the landscape of war. Most military earthworks in America were adaptations of European models, as were the armies themselves. As such, earthworks found on our Nation’s battlefield landscapes have connections to a long military tradition reaching back to classical times.
Archer Jones wrote in The Art of War in the Western World, “no Roman field force on the march ever camped without first entrenching according to a standard plan.” It was a practice that the Romans derived from the Greeks, who acquired it from the Persians before them. The Roman legions, however, differed from their predecessors by their habit of entrenching with relentless regularity and purpose. Within days they could encircle an enemy fortress with miles of earthen walls. In a few years they built Hadrian’s Wall, a seventy-two mile long, fifteen-foot rampart of turf to connect a series of stone forts in northern Britain. This frontier barrier, fronted by a ditch twenty-seven feet wide and nine feet deep, intimidated Celtic invaders for nearly two hundred years.
Although much expertise was lost with the collapse of the Roman Empire, many aspects of Roman siege craft survived into the Middle Ages. The independent well-sited castle with its high stone walls, which made attacks arduous affairs, dominated the medieval landscape. In order to breach such defenses, besieging armies had to get close enough either to construct towers to overpower the walls, smash through them with catapults and battering rams, or dig tunnels to undermine and collapse them. To employ any of these techniques it was necessary first to construct military earthworks, which allowed the besiegers to approach the castle walls under cover.
In the fifteenth century, the invention of gunpowder and moveable siege artillery ushered in a new era of warfare and fortifications. In 1494, these new technologies allowed Charles VIII of France to destroy a fortress in eight hours that had once withstood a traditional siege lasting nearly seven years. For the next two hundred years, military engineers struggled to devise an adequate defense against ever more powerful and more mobile artillery. Earthworks gained prominence over brittle stone and brick construction because earth could better absorb the impact of projectiles.
As a result, engineers designed ramparts, thick defensive walls of solidly tamped earth held in place by retaining walls of stone (called revetments) and fronted by a wide, deep ditch. From a distance, these fortifications presented a low profile to the enemy with only the protective parapet, atop the rampart, rising above ground level. This design proved a difficult target for enemy artillery. In addition, engineers reshaped the ground in front of the defenses, called the glacis, to form a gradual slope rising to the lip of the ditch to conceal the brittle masonry revetments. In essence, the engineers protected their defensive walls by burying them. Heavy artillery, mounted atop the ramparts, kept an attacker's siege cannons at a cautious distance.
Five principles determined the design of these low-profile defenses and continued to influence fortification theory into the twentieth century. According to the principle of equilibrium of defense, a fortress was only as strong as its weakest point, so engineers built every part to the same high standard. Second, each “fort” or artillery strong point was built within range of adjacent strong points; their defense was mutually supporting. Third, because artillerists and infantrymen instinctively fired their weapons directly to their front, engineers sited individual segments of the defenses perpendicular to the anticipated direction of fire. Each segment was responsible for defending only the sector to its immediate front. Also, engineers favored straight lines that forced all defenders of a sector to concentrate their fire in one direction. These considerations resulted in a more angular trace, or ground plan, that combined salient angles (pointing towards the attackers) with reentering angles (pointing toward the defenders). Fourth, engineers sought to eliminate dead ground—areas that could not be fired upon from within the fortress. With proper design, all ground in front could be fired upon from some part of the fortification. Fifth, engineers strove for defense in depth by building outlying rings of fortifications around the main fortress. Through these principles, the defense regained parity with the offense.

The core of these principles, the bastion system, became a standard component of artillery fortifications. A bastion is a four-part, angular projection, consisting of two salient faces oriented towards the enemy and two flanks that directed fire sideways across the faces of adjacent bastions. While a simple square or rectangular trace left large areas of dead ground directly in front of each angle, bastions allowed crossing fires of artillery or small arms to cover every approach.

Although he had many predecessors, the master of the bastion system was Sebastien le Prestre de Vauban (1633-1707). As Louis XIV’s chief military engineer, Vauban designed more than a hundred fortresses to defend the cities and frontiers of France. His complex, often star-shaped designs featured multiple layers of defense based on the geometry of interlocking fields of fire. At the heart of Vauban’s genius, however, was an instinctive understanding that a fortification’s design must be uniquely suited to the ground it occupied and that topography above all else drove design. Function determined form. Numerous imitators failed to grasp this basic precept and often sought to impose a specific design, regardless of topography, with inferior results.
But Vauban was not content merely to build fortifications; he sought the most judicious means to destroy them. He developed a systematic approach for capturing permanent fortifications by exploiting weaknesses in his own designs. In Vauban’s “scientific” method, a besieging army used earthworks offensively, first erecting a parapet parallel to the fortress beyond artillery range, and then digging a zigzag trench (a sap) toward the fortress at night. At the end of each sap, the army constructed another parallel until they could haul artillery forward under cover to bombard at close range. The army typically directed artillery against the salient angle of the weakest bastion where it eventually breached the walls and opened the way for an infantry assault. With Vauban’s system, military engineers could project the cost of a siege in troops and material and predict its duration to within a matter of hours.
Illustration of types of classic earthworks

Redan, lunette, bastion, redoubt, star fort - forthcoming

Vauban often added an outer ring of defenses, consisting of a series of individual earthworks built within supporting distance of one another. These detached outer works were intended to hold important terrain beyond the main perimeter, such as a hill, crossroad, or stream crossing, and to temporarily delay the enemy’s approach. It took fewer soldiers or cannons to man such defenses and the earthworks could be thrown up and as soon abandoned. Military engineers quickly adapted Vauban’s models to the needs of active campaigning. By the mid-1700s, armies regularly built detached fieldworks to defend depots, supply lines, and artillery batteries. With modifications, armies still use some of these models.
The simplest detached earthwork, called a redan, consisted of two faces thirty to forty yards long forming one salient angle (like an open “V” with the point toward the enemy). A redan was left open to the rear (or gorge), so that if an attacker captured it, defenders could fire directly into it from a secondary line. Adding a left and a right flank to a redan to protect against enfilade fire converts the earthwork into a lunette, consisting of three salient angles and an open gorge. (A lunette connected to another lunette with a curtain wall became a bastion.) The redoubt, a third common earthwork, is an enclosed polygon without re-entering angles. A redoubt is defensible on all sides. Depending on the length and number of faces, a redoubt can be sized to hold fifty or five hundred men. A fort, in theory, was a complex, enclosed artillery fortification that might incorporate a variety of forms. In practice, soldiers might refer to any artillery earthwork as “a fort.” A star fort is an enclosed earthwork that combines salient and reentering angles without bastions. A typical star fort would be constructed with eight “points” projecting toward the enemy.
The next advances in technology and strategy would be fully tested during the Napoleonic Wars (1800-1815). By the 1760s, the French Army mounted larger caliber, yet lighter, bronze tubes on wheeled carriages that could be maneuvered over rough terrain, an innovation that quickly spread to other European armies. In 1792, the British Royal Artillery attached these cannons to a light, easily maneuverable cart, called a limber, drawn by a team of six or eight horses. This resulted in a truly mobile artillery piece that could keep pace with infantry on the march and deploy quickly in the field.
European industrialization allowed larger armies to be organized, equipped, and supplied, so that during Napoleon Bonaparte’s reign, armies increased fivefold to number a hundred thousand or more. Battle lines that once contended on a fairly concentrated front might extend for several miles. In battle, where all else was equal, the side disciplined enough to sustain its formation and rate of fire, while bearing the shock of horrendous casualties, eventually overpowered the other side and drove them from the field with a bayonet charge. In the tactics of the time, field artillery delivered firepower where it was most needed—to protect a unit’s flanks or to blast gaps in the enemy's lines with grapeshot or canister.
Field artillery allowed armies of the Napoleonic era greater mobility. Although hard marching, maneuver, and surprise, rather than the siege and static defense of permanent fortifications, came to be viewed as the determining factors of a successful military campaign, Bonaparte never lost sight of the essential role of military earthworks in the strategy of offensive war. He wrote:

I would prefer to . . . ask whether it is possible to concert a war without fortresses, and to this my answer is ‘no’. Without depot fortresses we are unable to work out good plans of campaign, and without field fortresses (by which I mean posts that are proof against hussars and raiding parties) we cannot wage offensive war. Hence those generals, who, in their wisdom, have rejected fortresses, are the very ones who are driven to the conclusion that one cannot wage offensive war.
As Bonaparte implied, most earthworks of the period were prepared entrenchments (constructed in anticipation of need), used to defend towns, garrisons, and depots. But the armies also erected detached earthworks while in the presence of the enemy. Such rapid entrenchments primarily protected artillery from enemy fire, while infantrymen relied on “found” defenses, such as a sunken road, a walled farmhouse, or a convenient rise in the ground. The Duke of Wellington often ordered his infantry to lie behind the reverse slope of an elevation, concealed from view. When attackers approached, his soldiers rose up en masse and fired disciplined volleys at close range, which broke up the attack. Such tactics with smoothbore muskets of limited range, while effective, depended heavily on terrain.
Toward the end of this period, some officers began instructing infantrymen to entrench on the battlefield to protect themselves from artillery fire. Prussian General Gebhard von Blücher ordered his troops to throw up one- or two-foot parapets when confronting French artillery. A solid shot, bounding across the field would strike the parapet and deflect up and over the soldiers who lay behind it. Blücher’s shallow shelter trenches had another advantage. Rather than concealing his infantrymen behind a ridge, he could deploy them along its front, giving a view of the enemy and a clear field of fire. Soldiers had begun to provide their own cover on chosen ground.
Hunting rifles had been in use for generations but had a limited role in combat because they were slow to load. In the 1840s, the first mass-produced rifled weapons—both rifled artillery and rifled muskets—were introduced to the armies of Europe. The technology, spiral grooves incised in the gun’s barrel, imparted a stabilizing spin to a rifled projectile, making it more accurate at longer ranges and giving it greater penetrating power. Rather than a round ball, rifled artillery fired an elongated bolt designed to fit the barrel’s grooves. Rifled-muskets fired a hollow-base, conical bullet, called a minnie ball after its innovator, Claude Etienne Minié. Minnie balls made it possible to load and fire a rifled-musket as quickly as a smoothbore, and a rifled-musket’s effective range was three hundred yards—three times that of smoothbore muskets.
The use of rifled weapons expanded the lethal zone for infantryman. Against smoothbore muskets, an attacking force would approach within a hundred yards of a line of defenders before incurring serious losses, then make a last dash to close with the enemy. Against rifled-muskets, however, an attacking unit could rarely hope to cross the last hundred yards of open ground without tacking crippling casualties and losing cohesion. It became much more difficult to deliver the decisive bayonet charge prescribed by Napoleonic doctrine.
Significant numbers of rifled weapons were first employed in the Crimean War (1854-1856); it was also the first war to witness large-scale use of rapidly constructed entrenchments. This was not a coincidence. The increased range and accuracy of British and French rifled-muskets forced Russian troops, armed mostly with smoothbores, to abandon the direct assault and begin entrenching. Military theorists were still debating the lessons of rifled firepower and entrenchment when the American Civil War erupted. Although armies had used earthworks as a part of every American engagement beginning with the French and Indian Wars, the Civil War use of military earthworks was on an unprecedented scale, and by 1864 all the troops were regularly entrenching on the battlefield. For the first time in three centuries, the European “teachers” sent military observers to the United States to study the use of earthworks. As weapons improved, the profile of earthworks got lower and the ditches deeper, so that by World War I, the last war to rely almost exclusively on earthworks, the trench was the defining battlefield terrain feature.

II. An Annotated Chronology of American Military Earthworks

The following represents an abbreviated history of the development of military earthworks in the United States focusing on extant examples in the National Park system. These are highlighted in bold type. (Clicking on the name will hotlink you to the park expanded website.)
1562 Fort Caroline at the mouth of the St. Johns River, Florida. Perhaps the first fortification constructed in America. Built by the French as a defense against Spanish coastal raiders. Its designer, Rene de Laudonniere, described this triangular stockade, which overlooked the Saint Johns River near modern-day Jacksonville, Florida:

inclosed with a little trench and raised with turfes made in form of a battlement of nine foot high: the other side …was inclosed with a Pallisado of planks of timber … there was a kind of bastion within which I caused an house for the munition to be built (a magazine); it was all builded with fagots and sand, saving about two or three foot high with turfes ....

  1. Jamestown Island, Virginia. English settlers constructed a fort of similar design to defend against hostile Indians. As European settlement expanded into the interior, conflict with the native inhabitants increased. Settlers built palisade forts and blockhouses to protect trading posts, villages, and homesteads. Although effective against Indian forays, professional soldiers considered most of these defenses primitive—in architectural terms, vernacular.

  1. Castillo San Marcos, St. Augustine, Florida. The Spanish started work on America’s first European style masonry fortification. When completed twenty-three years later, the Castillo de San Marcos represented the classic model of a four-bastioned fortress with a flooded moat. British troops besieged the Castillo for nearly two months in 1702 but lacked the artillery to penetrate its defenses.

1675-1677 King Philip’s War. In 1676, inhabitants of Boston sealed off their peninsula with an earthwork and moat, an early example of an entrenched defensive line.

  1. Fort King George, (present-day) Darien, Georgia. To prevent Spanish incursions, the British built Fort King George of logs and earth where it served as the southernmost outpost of the British colonies until 1732.

1753-1763 The Seven Years War or French and Indian War. During the war there was widespread adoption of European fortification techniques in the colonies.

  • French Forts Niagara and Carillon (later Fort Ticonderoga) designed by Pierre Pouchet de Maupas. Ticonderoga was a rectangular, bastioned work with double log revetments filled with tamped earth and faced with cut stone.

  • English Forts Augusta, Ligonier, Mercer, and Pitt designed by engineer Harry Gordon. Fort Augusta was a large, rectangular earthen redoubt, Fort Ligonier a four-bastioned earthwork with double, horizontal log walls, filled with earth and topped with sod. Many forts of this period could be described as “dug” rather than “erected.” Five-bastioned Fort Pitt at the strategic confluence of the Allegheny and Monongahela Rivers was conceived on a grand scale (it encompassed 18 acres) but remained incomplete when the war ended.

  • Americans learned fortifications from British engineering manuals or by direct experience in the field. During Colonel George Washington's first expedition against the French and Indians in 1754, he ordered his Virginia militiamen to construct a log stockade flanked by an entrenchment at Great Meadows, Pennsylvania. This ideal campsite--with lush grass and plenty of water--proved a poor location for defense. The French with their Indian allies surrounded and fired into the fort from higher ground. Heavy rainfall then flooded the Virginians out of their entrenchment, forcing them to surrender. Colonel Washington’s inexperience with field fortification was not unusual among colonial officers.

1775-1783 The American Revolution. The Continental Army at the inception of the Revolutionary War was an amateur organization that gradually gained in sophistication and effectiveness. Fortifications played a crucial role in this development, and contesting military engineers—many of them Europeans—often decided outcomes. From the start of war with Britain, the Americans built earthworks—primarily artillery redans, lunettes, and redoubts—as defenses for harbors, towns, and garrisons. American officers looked to field fortifications to help equalize disparities between their poorly equipped regulars or untrained militiamen and the highly disciplined British army. But trained engineers were scarce. Self-taught novices were pressed into duty, often armed with little more than a British or French instruction manual. As a result, many early earthworks were poorly sited or crudely constructed. “The skill of those engineers we have is very imperfect,” Washington complained to Congress in 1775, “ . . . whereas the war in which we are engaged requires a knowledge comprehending the duties in the field and fortifications.” Washington recognized that he would need to meet and overcome superior British engineering.

The French Minster of War “loaned” four military engineers to the Continental Army in 1777, including Louis le Begue de Presle Duportail, who remained Washington's chief of engineers for the rest of the war. Duportail supplied essential technical skills and worked throughout the war to establish and train a corps of engineers along with companies of “sappers and miners” to build field fortifications for the army. Duportail and his engineers designed works at Philadelphia, Wilmington, Boston, Valley Forge, West Point, and Yorktown.

In late 1778, the British shifted their principal efforts to the coasts of Georgia and the Carolinas. An amphibious force captured Savannah in December and, from this fortified enclave, soldiers marched into the interior to occupy Augusta. In March 1779, the British moved against Charleston but were unable to penetrate its defenses. Forts Sullivan, Moultrie, and Johnson—all constructed of double revetments of palmetto logs filled with sand—repelled the ships that attempted to enter the harbor. The land approaches were defended by a line of earthworks fronted by a substantial moat that stretched between the Ashley and Cooper Rivers. A prominent masonry “hornwork” held the center of the line.

British General Henry Clinton returned a year later, in March 1780, with enough force to besiege the town. His engineers first constructed a line of works across the Charleston Peninsula and over six weeks opened a series of parallels in the manner prescribed by Vauban. British sappers dug within yards of the American line and worked at night to drain water from the moat. The garrison surrendered on May 10, when it was apparent that Clinton was prepared to assault the weakened defenses.

In spring 1781, the tide turned. British fortified outposts in the interior began falling to the forces of Nathanael Greene. In May, Greene captured Fort Grierson and lay siege to Fort Cornwallis—the principal defenses of Augusta. His soldiers scoured surrounding farms for entrenching tools. Over the next two weeks, the Americans advanced saps and parallels and built a large artillery platform, called a Maham Tower, to fire into fort. Despite an energetic defense, the garrison surrendered on June 5. In the meantime, Greene sent part of his force to lay siege to the eight-pointed star fort and entrenched depot at Ninety Six.

About 550 regulars and Loyalist militia and a labor battalion of liberated slaves fearing recapture held the Ninety Six defenses—laid out by Lord Cornwallis’ engineering officer, Lieutenant Henry Haldane. For nearly three weeks, the garrison countered every attempt to subdue the fort by raising the height of the parapets, erecting a sixteen-foot high traverse to protect the fort’s interior, and sallying forth nightly to disrupt the entrenching. Under the direction of Kosciuszko, the Americans completed several advanced breaching batteries, opened a third parallel within rushing distance of the fort, and began a tunnel to undermine the salient angle. After a costly frontal assault failed on June 18, Greene abandoned the siege at word of approaching British reinforcements.

In September 1781, the French Army contingent under Comte de Rochambeau joined the Continental Army to besiege Lord Cornwallis' army, which had dug in at Yorktown, Virginia. While a French fleet sealed off Yorktown from the bay, Rochambeau’s engineer Colonel Desandrouins and Louis Duportail of Washington’s staff directed the siege. On October 9, heavy guns, borrowed from the French fleet, opened fire from a first parallel. The sappers opened a second parallel five days later and positioned nearly a hundred cannons to batter the British defenses. When bayonet assaults carried two outlying redoubts, the defenders’ situation grew desperate. Cornwallis surrendered his army on October 18, and the British government entered negotiations to end the war. This sophisticated siege would have been unthinkable earlier in the war and impractical without French artillery and engineering.

    1. First System of coastal defenses. These fortifications, authorized by the fledging United States government, were built primarily of log revetments filled with earth.

  1. United States Military Academy established at West Point as a training school for military officers and modeled after European military academies, such as France’s l’Ecole Polytechnique, where civil and military engineering were the cornerstones of the curriculum.

1804-1812 Second System of coastal defenses—many replacing earlier fortifications—were designed as multi-story artillery platforms with the guns enclosed in heavy masonry casemates. In some ways, these forts were a throwback to the high stone walls of the medieval castle but were justified because their purpose was to deliver a high rate of fire against vulnerable wooden ships. Detached earthworks were often added to strengthen land approaches. West Point graduates inducted into the Army Corps of Engineers undertook this work.

1812-1815 War of 1812. At the outbreak of the war only a few of the proposed Second System forts were completed. Redans, lunettes, and redoubts were thrown up as temporary measures to protect ports and rivers. Nonetheless, America's fledgling coastal defenses garnered respect from the blockading British Navy. According to British naval officers, Fort Warburton (later Fort Washington), which guarded the Potomac River route to Washington D.C., might seriously have delayed their fleet had its garrison not decamped without firing a shot. The heroic defense of Fort McHenry in Baltimore Harbor, on the other hand, turned back a British naval expedition on September 13, 1814. Numerous coastal earthworks, such as Castle Williams in New York, deterred British parties from landing at will and inflicting additional damage.

Much of the land war was fought along the western and Canadian frontiers to control the principal forts of the region. These forts ranged in construction from simple log stockades with corner blockhouses to bastioned forts of double log revetments filled with earth. Although soldiers often threw up detached artillery works—redans and lunettes—they rarely entrenched on the battlefield. The Battle of New Orleans at Chalmette in 1815 was a notable exception. When a strong British army marched on the city along the bank of the Mississippi River, Andrew Jackson ordered his army of citizen soldiers—militia, gentry, slaves, tradesmen, Creoles, Indians, and pirates—to entrench across its path. At first an ad hoc affair thrown up behind an old canal, these earthworks were strengthened over the course of a week into an imposing barrier under direction of Jackson’s chief engineer, Arsene LaCarriere Latour. The resulting line, consisting of sections of parapet interspersed with seven batteries, reached from the river inland for about a mile, anchoring there on a cypress swamp. In some places, the parapet was twenty feet thick with the canal in front deepened to twelve feet. Elongated sacks of compressed cotton were used to form revetments for the batteries, giving rise to stories that the Americans fought from behind cotton bales. Jackson’s fortifications served their purpose, allowing his militiamen to inflict crippling causalities on the British regulars.

1816-1866 Third System of coastal defenses. Lt. Colonel Joseph G. Totten (1788-1864) was considered the foremost fortification designer of this period. By the start of the Civil War, more than thirty forts were completed, though not all were fully armed. Third System examples in the National Park Service include: a renovated Fort McHenry (Baltimore), Fort Washington (Washington DC), Fort Sumter (Charleston), Fort Pickens (Pensacola), Fort Jefferson (Dry Tortugas), and Fort Winfield Scott (San Francisco).

When completed in 1847, Fort Pulaski at the mouth of the Savannah River was considered the “ultimate defense system” of its time and as impregnable as the “Rocky Mountains.” Georgia State militia seized the fort in January 1861 and Confederate troops garrisoned it until the arrival of a Federal expeditionary force in February 1862. Projectiles from ten experimental rifled guns, firing from Tybee Island more than a mile away, bored into and began shattering the eight-foot thick solid brick walls in only thirty hours of bombardment. The brittle “castle” walls had fallen once again to improved artillery; the ultimate defense of 1847 was obsolete by 1862. Earthen forts, such as the massive Fort Fisher south of Wilmington, North Carolina, were shown later in the war to be nearly impervious to bombardment.

  1. A Treatise on the Science of War and Fortification published. John Michael O'Conner, engineering instructor at West Point translated two key French works: French engineer Guy de Vernon’s manual of the same name with a hundred-page summary of Baron Henri de Jomini's Traité des Grandes Operations Militaire.

1836 A Complete Treatise on Field Fortification, with the General Outlines of the Principles Regulating the Arrangement, the Attack, and the Defense of Permanent Works by Dennis Hart Mahan published. Mahan, who replaced O'Conner at West Point in 1824, taught for forty-seven years, making him perhaps the most influential American military engineer of the nineteenth century. Nearly every West Point graduate who served in the War with Mexico, the Civil War, and the numerous Indian Wars learned basic fortification theory and method from Mahan.

Because the regular army was small and scattered among frontier outposts, Mahan reasoned that future wars would be fought with volunteer armies, trained and led primarily by West Point officers. He believed the volunteers would initially have to rely on field fortifications to even the odds against a foreign professional army and that their training in entrenchments would require easily understood and profusely illustrated instruction manuals. Therefore, he wrote his text “in a manner to be within the comprehension of any person of ordinary intelligence.” Mahan’s first edition summarized the most current European theories of field fortification, and from his detailed descriptions and diagrams a novice could build an earthwork to suit most situations. Mahan published three editions of Field Fortification before the Civil War. In the introduction to his third edition in 1861, Mahan predicted that the increased range and accuracy of rifled weapons would radically change the face of warfare. “The great destruction of life in open assaults by columns exposed within so long a range,” he wrote, “must give additional value to entrenched fields of battle.” The battlefields of the American Civil War became the proving ground for Mahan’s theories.
1861-1865 The Civil War. American officers entered the Civil War with two conflicting military doctrines. The first hearkened back to Napoleon’s reliance on mobility, surprise, and attack; the second favored the entrenched defense. In Jomini’s terms, the debate was between a “modern” system of rapid marches and the old system of a war of positions. Army officer Ora E. Hunt, wrote that:

At the beginning of the Civil War, the opinion in the North and South was adverse to the use of fieldworks, for the manual labor required to throw them up was thought to detract from the dignity of a soldier. . . . The epithet of dirt-diggers was applied to the advocates of entrenchments. Expressions were heard to the effect that the difference ought to be settled by a fair, stand-up fight in the open.
By 1864, “dirt diggers” predominated on the battlefield, whether due to war weariness or to combat experience. Paddy Griffith has suggested that both sides fell into “an escalating spiral of ritualistic trench-building” that eventually strangled the doctrine of mobility—all due to the overweening influence of Mahan and his trench-obsessed engineers; the spade ousted the bayonet because of a failure of discipline and loss of the will to attack. The fact remains that rapid entrenchments, ritualistic or not, significantly improved the combat value of the landscape. Defenders increased the effectiveness of their fire and their survival odds by digging. Most units entered the war armed with smoothbore muskets, but by 1864, both sides had equipped their front-line troops with rifle-muskets. A few elite Federal units carried expensive repeating rifles—Spencers and Henrys—that could lay down a tremendous volume of fire. Entrenching, for the common soldier, was a rational response to the increasing lethality of the battlefield.

Because military earthworks and the Civil War are inseparable, there is no easy synopsis of the critical role this technology played in the progress of the war. Mahan’s prediction that entrenching would dominate future American battlefields had its proof in the Civil War landscape. It is true that the type of earthworks constructed during the Civil War looked backward to the eras of Vauban and Napoleon as much as they heralded future efforts. By the war’s end, as witnessed in the siege of Richmond and Petersburg, the world was offered a sobering glimpse into European trench warfare of the early twentieth century, although machine guns, smokeless gunpowder, and high explosives—not to mention poisonous gas—were still distant terrors. (Click here for more the expanded history of military earthworks and the Civil War.)

1870- Present Following the Civil War, American soldiers often resorted to rifle trenches and foxholes in their struggles against the Plains Indians. Engineers reverted to a reliance on earthworks for coastal defense and no new masonry forts were constructed. The dispersed low-profile shore batteries of the Endicott Period (1890-1910) that continued through World Wars I and II were primarily earthworks with extensive concrete reinforcement and various armaments. With the rise of airplanes, submarines, and cruise missiles, these fortifications have been abandoned and are falling into ruin. Yet modern military manuals continue to explain how to construct earthen field fortifications. In the Vietnam War, entrenched firebases with sandbag parapets and interlocking fields of fire had much in common with nineteenth century prototypes. The Gulf War brought chilling images of enemy combat bulldozers smothering Iraqi soldiers with their own parapets. Earthworks continue to be an integral part of warfare, and soldiers have much to learn from studying battlefields of the past.

Today, historians study military earthworks for several important reasons. First, earthworks are an irreplaceable archeological resource handed down by thousands of common soldiers who marched, fought, labored, and died in the ranks for countries and causes. The American people cannot afford to lose touch with these sites of commitment and sacrifice. Second, earthworks provide hard evidence of the locations, numbers, and deployments of units during certain phases of a battle. To interpret a battle, historians rely heavily on written descriptions by participants, but after-action reports are often self-serving or confused by the war’s fog and are often at odds with the archeological record. There is no refuting remnant earthworks. Third, military earthworks reveal the logic (or confusion) of the officers and soldiers who designed and constructed them. The engineers who directed and the soldiers who constructed earthworks transformed peaceful social landscapes into places of violence. Those who knew their trade could fashion nearly impregnable defenses from the ground. Their task was to prevent the deaths of their own but at the same time deliver death to others. As such, earthworks reveal the underlying architecture of combat—an architecture that changed from place to place according to the terrain, the weaponry, the numbers and experience of the soldiers. Fourth, earthworks provide examples of advances in military engineering. The classical models shown in the manuals and the theories underlying their construction continued to develop over time and in the face of battle. Comparing survival records from various military eras is a very good way to understand the successful evolution of fortification design. Finally, surviving earthworks enable the interpretation and story telling associated with an event and for explaining a community's role in the nation’s warfare. Preserved earthworks provide a focus for landscape preservation activities, not only in the national parks, but in local communities, as well.

Much that appertains to the Engineer’s Art is but an affair of feet and inches; facts which are the results of long usage, holding, in many instances, the important position of principles. His experience has taught him that those authors are the clearest who enter into the minutiae of their subject; and that with pupils of superior minds, a thorough knowledge of details is an invaluable aid in unraveling the difficulties, and retaining the principles of the Art; whilst, with those of limited capacities, a want of such detail leaves them with the most vague and unsatisfactory notions. --Dennis Hart Mahan, 1863

A History of Earthworks in the United States Lowe and Hawke, Draft 2/2/00

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