United States Army Engineers devoted more time, resources, and effort to defend Washington, D.C., from enemy attack than any other single enterprise during the American Civil War. Over the course of the rebellion, they continually expanded and improved the defenses to meet new demands and achieve greater levels of security in the face of a determined and aggressive foe-primarily Robert E. Lee and his Army of Northern Virginia. Initially the city's defenses were only effective when garrisoned by a large force and really served as a line of last resort in case of defeat in the field. Eventually the growing strength of Washington's defenses allowed Union commander Lt. Gen. Ulysses S. Grant to operate completely on the offensive without having to employ his field troops to guard against an attack on the capital. Therefore, the defenses of Washington not only served to protect the nation's capital but ultimately allowed federal forces to go on relentless offensives that eventually brought an end to the war.

Of the myriad military engineer duties, especially in times of war, defending capital cities was one of the most important and oftentimes the most difficult. Capital cities were inherent population centers but were also home to the buildings, records, workers, and leaders required by governments to operate. Strategically, their capture would deal a severe blow to a government's ability to function. Psychologically, their preservation served as bulwarks in the face of adversity while their capture was infinitely more demoralizing than any defeat in the field-taking them would likely have occurred only after the complete annihilation of or retreat by their defenders. In an ironic twist, it was the southern states that influenced the decision to establish the United States' capital on the banks of the Potomac River after the American Revolution (rather than in a northern city), a decision which then also doomed it to an uncomfortable proximity to those same southern states when they seceded from the Union in 1860 and 1861. Therefore, Washington, D.C., and Richmond, Virginia, its counterpart for the Confederates States one hundred miles south, became like so many European capitals during the Napoleonic Wars-close to the enemy and immeasurably important because the capture of either would likely have led to a swift end to the war.

Before the American Civil War, the U.S. could count only 120 Army Engineers-a small cadre of the Army's top West Point graduates whose roles were as diverse as their duty stations across the rapidly-expanding nation. They were highly respected sea coast defenders, surveyors, explorers, naturalists, hydrologists, builders, and military strategists. In times of war, however, the country still depended on temporary volunteer forces, raised locally, to serve their states' defense. Known as Regulars, the permanent members of the U.S. military, including the engineers, did not lead the volunteer state forces unless they left the regular army. Whether seeking opportunities for promotion or battlefield experience, when the Civil War broke out, many engineers took leave of the regular ranks to lead volunteer units into battle. Others resigned their commissions to take up arms with the rebelling Confederacy, leaving only thirty engineer officers on duty by the time of the first battle of Manassas in July 1861. For those who remained, roughly half were assigned to protect the Union capital from enemy attack. Only a few hundred yards separated essential U.S. government buildings, including the White House, from Arlington Heights in enemy territory in Virginia. If the United States was going to keep its capital in D.C., then it would require its finest engineers to defend it.

Unfortunately for its defenders, the District of Columbia has no natural defensive features that could have been easily adapted into fortifications. The city sits in a shallow bowl along the confluence of two rivers, surrounded on all sides by low hills. The Potomac and Anacostia rivers are narrow and fordable upstream from the city, rendering them defensively inferior to the great rivers of Europe. The city's surrounding hills could also allow an enemy force to shell the city from a distance of three to four miles easily without even necessitating a river crossing. Therefore, engineers completely disregarded the city limits when locating fortifications to protect the capital in the spring of 1861. Instead, they sought to occupy the highest ground possible to deny it to the enemy while claiming a superior vantage point to detect and fire upon them. Unfortunately, most of the best sites were in Virginia, which in April and May of 1861 was embroiled in a secession debate. To avoid provoking the uneasy Virginians, engineers made initial observations and site surveys from the ends of the three bridges that carried roads across the Potomac between D.C. and Virginia-Long Bridge (roughly located near today's 14th Street Bridge), the Aqueduct Bridge (located very similarly to today's Key Bridge), and the Chain Bridge. In fact, the purpose of the fortifications planned first was to protect the bridges from enemy assault. At the same time, engineers also began rehabilitating the only permanent fortification in the region-Fort Washington, twelve miles south of D.C. on the Potomac River in Maryland-to protect Washington from maritime invasion.

In late May of 1861, in the wake of the Confederate attack on Fort Sumter in South Carolina and Union President Abraham Lincoln's call for volunteer forces from every state to put down the rebellion, Virginians finally voted to secede from and take up arms against the United States. Lt. Gen. Winfield Scott, the 74-year-old commanding general of the United States Army, urged Lincoln to occupy the nearby rolling Virginia countryside from where Confederate artillery could shell the city and stage troops for a frontal invasion. Heeding the warning, Lincoln ordered three columns of troops, along with engineer and artillery officers, to cross the Potomac in the first offensive movement of the war. In the early morning of May 24, 1861, Capt. W. H. Wood via the Aqueduct Bridge, Col. Samuel Heintzelman by Long Bridge, and Col. Elmer Ellsworth by boat into Alexandria all crossed the Potomac into Virginia. The engineers assigned to these parties were Cpt. D. P. Woodbury, Lt. O. E. Cross, Cpt. B. S. Alexander, Lt. F. E. Prime, and Cpt. Horatio G. Wright. The infantry traveled with entrenching tools and immediately began constructing Forts Runyon and Corcoran, which had been sited based on the earlier reconnaissance from the ends of the bridges.

Upon the high ground that overlooked the city, engineers quickly identified additional suitable locations that commanded the local countryside, made for good natural defensive positions, and would protect the city from an artillery barrage. The following day, the infantry soldiers began entrenching. For seven weeks they surveyed, cleared trees, and built earthen lunettes and redans until they had created a jagged line of defenses along Arlington Heights opposite the city and separate fortifications to protect each of the city's three bridges. These early earthworks generally consisted of six-foot-high embankments fronted by twelve-foot-wide and eight-foot-deep trenches with openings at the top for artillery and banquettes for infantry fire. Initially the defenses were not strong enough or adequately interconnected to withstand strong frontal assaults, to prevent small raiding parties from infiltrating the city, or to endure long-term sieges. Instead, they acted as a series of defensive works to support and protect Union armies in case of their defeat in the field. In the event of a rout, troops could fall back to the line and make the passage of an enemy army extremely difficult.

After their seven weeks of preparation, federal forces put their strategy to the test. In July 1861, Gen. Irvin McDowell moved the Union Army of the Potomac into Virginia beyond the defensive works to meet Confederates in the field at Manassas Junction. Only thirty miles from D.C., federal forces suffered their first defeat in the theater and promptly moved back to the defenses around Washington. Although eager to pursue their foes and possibly put a swift end to the war, the Confederate leadership deemed the defensive works to be too strong to assail. For the remainder of 1861, the defenses of Washington fulfilled their initial purpose by allowing a demoralized Army to recoup in relative safety.

Shortly after the initial defeat at Manassas, Lincoln appointed former Army Engineer Maj. Gen. George B. McClellan as the new commander of the Army of the Potomac. McClellan recognized the importance of strong defenses for the capital city and appointed Maj. John Gross Barnard as the chief engineer of his army. Together they began strengthening the city's defenses while federal forces prepared for their next offensive. Over five months, from August to December 1861, Barnard oversaw the expansion of the jagged line into a defensive system that could withstand a full frontal assault by adding connecting trenches, twelve-foot-tall anti-cavalry chevaux-de-frise in their fronts, and additional redoubts for gun emplacements and banquettes for infantry. Barnard increased the number of fortifications on the Virginia side to ensure each was within cannon shot of one another and expanded the system into Maryland to protect some of the major approaches from the north and west. By the start of 1862, the defenses of Washington spanned roughly 35 miles and included 37 forts and 443 artillery pieces. To build his system, Barnard employed fifteen officers of the Corps of Engineers, by far the agency's largest effort of the war, along with hired men, freed slaves from nearby plantations, and military convicts. Despite using the cheapest labor available, Barnard's labor costs routinely ran over budget and by the end of the war had amounted to roughly $1.5 million.

After McClellan's 1862 campaign ended in defeat on the outskirts of Richmond, Barnard continued to lobby the War Department for an even stronger defensive system to protect the nation's capital. During the Antietam campaign Lee and his Confederate Army demonstrated that they could indeed take the war north of the Potomac and therefore could seriously threaten Washington via routes other than those through Arlington and Alexandria. Barnard wished to strengthen the defenses along the northern approaches to the city and improve the roads, communication lines, and infantry breastworks between the existing fortifications. He now envisioned a seamless line of nearly impenetrable defenses that would fully encircle the city with large earthen forts every 800 to 1,000 yards. To many, Barnard's plan seemed unnecessary and exorbitantly expensive, but in light of Lee's advance into western Maryland in the fall of 1862, Secretary of War Edwin Stanton was at least willing to appoint a board of engineers to determine the effectiveness of the current defenses and to study the feasibility of Barnard's plan. On October 25, 1862, the secretary appointed a commission consisting of Chief Engineer Brig. Gen. Jospeh Totten, Quartermaster General and former engineer Brig. Gen. Montgomery Meigs, Chief of Artillery Brig. Gen. W. F. Barry, and Brig. Gen. George W. Cullum of the Corps of Engineers who was then serving as Chief of Staff for Lt. Gen. Winfield Scott. Secretary Stanton appointed Barnard to the commission as well. Together, some of the best engineers and artillerists in the nation spent the next two months studying the existing forts and the terrain before making a final recommendation.

In their report, the commission divided D.C.'s defenses into four groups. The first group included those along Arlington Heights opposite Georgetown and the Aqueduct Bridge to below Alexandria south of the Potomac River. The second was the small group of fortifications that protected the approaches to the Chain Bridge north and west of the District of Columbia. The third consisted of the defensive works in Maryland between the Potomac River near Little Falls to the Anacostia River along Bladensburg Road. The fourth was the line between the Anacostia at Benning Road south to the Maryland shore opposite Alexandria. At the time the report was drafted, the number of forts totaled 53; an additional 22 batteries supported 643 guns and 75 mortars. The commission recommended that 9,000 trained artillerists live within the forts to man their guns; that 25,000 infantry soldiers be encamped in central locations; and that 3,000 cavalry riders serve on outpost duty to warn of approaching enemies. In addition to recommending improvements for some of the existing forts, the commission advocated for no less than seven additional fortifications in the first group along Arlington Heights, for two to three more small works in the second group, for additional batteries in and opposite Alexandria to protect against maritime invasions, and for several small forts to connect the existing works in Maryland. Agreeing with their recommendations and understanding the importance of the defenses, Secretary of War Stanton sanctioned the expansion, which began in earnest in early 1863. The improvements were serviceable by the beginning of the spring campaign season and were almost entirely complete by the end of the year. Much like the previous year, 1863 witnessed a Union defeat along the banks of the Rappahannock River in central Virginia and an invasion of the north by Lee's army. But also in similar fashion, Lee retreated back to Virginia after his defeat at Gettysburg, having never tested the defenses around Washington.

With the commission's recommendations implemented by the end of 1863, the work in 1864 consisted mainly of fine-tuning the now sixty-eight defensive works. When Lt. Gen. Ulysses S. Grant, as of March 1864 the new commander of federal forces, departed on his spring campaign, John Barnard accompanied him as his chief engineer, leaving Lt. Col. B. S. Alexander in charge of the works surrounding D.C.  According to Barnard, the defenses of Washington, having evolved from "a few isolated works covering bridges or commanding a few especially important points," by 1864 were truly a "system of fortification by which every prominent point, at intervals of 800 to 1,000 yards, was occupied by an inclosed field-fort, every important approach or depression of ground, unseen from the forts, swept by a battery for field guns, and the whole connected by rifle trenches . . . furnishing emplacement for two ranks of men and affording covered communication along the line."1 Furthermore, the engineers had built roads wherever necessary to move troops and artillery from central points to anywhere on the periphery, all completely out of view of an approaching enemy. The ground in front of the defenses was stripped of its timber for one to two miles, and infantry used the wood to create rows of protective abatis. Each fort contained impenetrable "bombproofs" to store ammunition and to provide quarters for their defenders along with deep wells for convenient potable water. By 1864, the former line of "isolated works" more closely resembled permanent fortifications than hastily-built earthworks, and some of the largest, like Fort Runyon, measured 1,500 yards along their perimeters. Alexander was confident the system could now withstand a frontal assault by a large force of attackers, prevent any raids into the city, and withstand a prolonged siege. The only difference between the defenses of Washington and permanent fortifications was the lack of masonry reinforcement on exterior walls, which therefore limited the heights of the forts. Despite that limitation, Washington, D.C., was protected by a line of defenses unmatched in modern warfare.

Strategically, the defenses of Washington allowed a relatively small force to defend the capital in the face of a much larger enemy. Therefore, northern armies were unburdened of the need to remain between Lee and D.C. and became free to go on the offensive, an ability that became a significant advantage to the Union in 1864 and 1865. Grant might have been relentless regardless of the strength of Washington's defenses, but he remained free from having to worry about the capital and used every available soldier and gun for his pursuit of Lee in Virginia. By early June 1864, Grant had fought his way through central Virginia and around the Confederate capital and was positioned south of Richmond near Petersburg with Lee's army to his north and west, actually between him and the city of Washington. Petersburg was a major supply hub for Richmond, and Grant knew Lee would need to defend it as well to prevent the Confederate capital from falling. Aware of Grant's position and the lack of federal forces between Richmond and D.C., Lee believed a diversionary strike north of Grant's army might coax him to disengage. Lee selected Jubal Early and his corps of roughly 20,000 men to lead the diversion. They slipped west from Lee's ranks on June 13th and headed for the Shenandoah Valley, which offered excellent defensive cover and led directly to one of the Potomac River's major crossings at Harper's Ferry, West Virginia. Early's men dispersed the valley's federal defenders and were poised to move on Washington by early July. On July 6, 1864, his forces crossed the Potomac into the Maryland countryside to a location that afforded a straight shot down Rockville Pike to the nation's capital. A small Union force under Gen. Lew Wallace was able to delay Early's advance, but on July 10th, D.C. residents could see dust rising along the horizon from the advancing Confederate columns.

Grant's insatiable appetite for troops to pursue Lee through Virginia had depleted the ranks of the forces defending Washington. Grant had called upon the well-trained garrisons that had manned the fortifications for several seasons to join him in the field, leaving D.C. with woefully under-trained recruits. The fortifications were also manned at a level well below the recommended minimum of 40,000 defenders. Alexander noted empty block houses and unmanned batteries, while Barnard estimated total manpower at roughly 20,400 men. Of that number, 9,600 were raw recruits and 8,300 were part of the Veteran Reserve Corps (previously called the Invalid Corps), a group of disabled and previously wounded or ill soldiers who had been declared unfit for duty on the front lines. On July 9th, two divisions of Gen. Horatio Wright's Sixth Corps were ordered from Baltimore to help defend Washington, as were elements of the Nineteenth Corps, which had just returned to Fort Monroe, Virginia, from Louisiana. Without seasoned troops yet at the city's disposal, Maj. Gen. Henry Halleck ordered Maj. Gen. Alexander McCook to organize the Veteran Reserve Corps along Piney Branch Creek, about halfway between the city and the fort ring where they could have swift access to several of Washington's defenses. Col. Alexander rode out to meet McCook on July 10th to examine the defenses with him, as McCook had never even seen the works he was now assigned to defend. During the night, small bands of Veteran Reserve Corps troops, the Second District of Columbia Volunteers, and two artillery companies streamed into the Piney Branch camp. Early in the morning, McCook moved his available infantry into the rifle trenches on either side of Fort Stevens located within the present-day Washington neighborhood of Brightwood near the intersection of Georgia and Missouri Avenues. Other bands of federal forces, including roughly 2,000 Quartermaster Corps employees hastily armed and organized by former Army Engineer and then Quartermaster General Montgomery Meigs, moved into adjacent works and also waited to see where Early would strike.

Around 11:00 on the morning of July 11th, signal officers at Fort Reno observed clouds of dust and enemy wagons moving from the direction of Rockville toward Silver Spring, Maryland. By noon, Confederate Gen. Jubal Early and his cavalry, riding out ahead of his infantry, arrived within sight of Fort Stevens. Early found the works to be "but feebly manned" and believed he could take the fort if he pressed his attack quickly.2 He deployed a strong line of skirmishers to advance toward the fort, but their advance was checked as the cannons from Forts Stevens, Slocum, and DeRussy opened fire upon them. Receiving word of the Confederate whereabouts, six hundred dismounted federal cavalry soldiers arrived at Fort Stevens to shore up its defense. According to Early, "we saw a cloud of dust in the rear of the works toward Washington, and soon a column of the enemy filed into them on the right and left, and skirmishers were thrown out in front, while an artillery fire was opened on us from a number of batteries. This defeated our hopes of getting possession of the works by surprise."3 Incapable of taking the forts with only his advanced guard, Early sent scouts to reconnoiter the fortifications for a possible point of attack with his full force. What Early learned of the fortifications bewildered him:

"They were found to be exceedingly strong, and consisted of what appeared to be inclosed forts for heavy artillery, with a tier of lower works in front of each pierced for an immense number of guns, the whole being connected by curtains with ditches in front, and strengthened by palisades and abattis. The timber had been felled within a cannon range all around and left on the ground, making a formidable obstacle, and every possible approach was raked by artillery. On the right was Rock Creek running through a deep ravine, which had been rendered impassible by the felling of timber on each side, and beyond were the works on the Georgetown Pike, which had been reported to be the strongest of all. On the left, as far as the eye could reach, the works appeared to be of the same impregnable character. The position was naturally strong for defense, and the examination showed, what might have been expected, that every appliance of science and unlimited means had been used to render the fortifications around Washington as strong as possible."4

At roughly 4:00 in the afternoon, Maj. Gen. Horatio Wright and his veteran Sixth Corps troops arrived. About 900 of them were immediately deployed as skirmishers in front of the works, while 2,800 convalescents and some additional artillerists also arrived and were placed in reserve. McCook and his ragtag assembly of raw recruits, wounded veterans, and only a few hundred experienced soldiers were able to repel Early's most serious threat thus far. By the next day, Union forces were well in place and ready to take the brunt of the Confederate assault.

On July 12th, President Lincoln, Secretary of War Stanton, and Secretary of State William H. Seward came to Forts Stevens and Reno to observe the Confederate lines, the defenses of Washington, and the impending battle. That day, Early's forces occupied several points from where they could fire upon the fortifications, but they never attempted a frontal assault, which Early believed "would have been worse than folly."5 At 6 p.m. a brigade of the Sixth Corps attacked Early's position and drove the Confederates back; the encounter resulted in 280 men killed or wounded. That night Early disengaged and withdrew from the area, convinced that the defenses of Washington were truly unassailable and that lingering any longer would jeopardize his entire force. As he retreated, he burned the homes of federal officials near Silver Spring, Maryland, as a consolation and was comforted by having given the capital city, its residents, and the federal government a "terrible fright."

By deflecting Early's raid, the defenses of Washington had served their intended purposes-they allowed a smaller force to repel a larger one and gave the enemy few options for advancement while providing the Union forces the means for swift communication and movement from place to place. Importantly, the defenses also allowed Grant to continue applying constant pressure on Lee's army around Petersburg and Richmond. Early's excursion was the only challenge to D.C.'s fortifications, and Lee's gamble failed. Within a year, his army surrendered after being dislodged from around the Confederate capital. After the war, nearly all the fortifications became unnecessary. The Army retained only Fort Whipple and its environs, which already sat on federal land confiscated from Robert E. Lee's Arlington plantation. Fort Whipple was eventually renamed Fort Myer and is still operating today. By 1866 most remnants of the other forts vanished. At the end of the war the 68 forts, along with 93 batteries and 20 miles of infantry trenches, were auctioned off and their grounds reverted to the fields, farms, and forests whence they came.

One of the enduring legacies of the defenses of Washington is the outstanding thirty-mile system of military roads that the Union Army built throughout northern Virginia and the northern reaches of the District of Columbia, roads that became important thoroughfares in the region's modern transportation system. Engineers and infantry troops built the original Military Road in Arlington County over the course of three days, but it and its extensions remained major arteries in northern Virginia for decades. Built to service the fortifications that protected the southern approaches to D.C., Military Road in Arlington later became an essential connection from the 14th Street Bridge (Long Bridge) and the airport at Hoover Field to Arlington National Cemetery, Wilson Boulevard, north to Cherrydale, and on to Chain Bridge. Although few parts of the original road remain, in the area southeast of Cherrydale it roughly followed the line of present-day Route 29 east toward the Potomac River and then Route 110 south as far as Ronald Reagan Washington National Airport. In D.C. most of the military roads constructed in an arc from behind the forts near Little Falls over to the area adjacent to Fort Lincoln on Bladensburg Road have been superseded by the city's grid of urban streets. During the Civil War those roads traversed areas that were heavily forested or covered by fields and streams rather than densely populated neighborhoods. Today portions of Military Road NW still extend across Rock Creek west from Fort Stevens toward Tenleytown.

The remaining military roads and fort parks are today faint reminders of an anxious wartime D.C. But arguably the greatest national landmark that has endured the passage of 150 years since the war is Arlington National Cemetery. Robert E. Lee's 1,100-acre Arlington plantation, for which the heights it sat atop were named, was one of the first properties occupied by federal forces at the commencement of the war. An essential component of the defenses of Washington, Arlington House upon Arlington Heights served as Gen. George McClellan's headquarters as he built up the fortifications and rebuilt the Union Army between 1861 and 1862. Over the course of the war, engineers built two large fortifications on the plantation-Forts Whipple and McPherson-along with the smaller Fort Cass. When Quartermaster General Montgomery Meigs, a former colleague of Robert E. Lee, was tasked with finding a suitable place to bury federal troops who had perished in D.C. hospitals and on northern Virginia battlefields, he too looked to Arlington Heights. The fields of the former plantation that were not being used for defense or infantry camps became the site of temporary military hospitals, and Meigs thought it appropriate and convenient to allow those who perished there to remain. Not only did burying Union dead near the home of their enemy deprive the Lees the chance of ever returning, the grounds backed up to heavily-guarded defensive positions, meaning there was ample Army labor nearby to convert the plantation into a national cemetery. After the war, the cemetery was expanded to include the area once occupied by Fort McPherson, now Section 11, which added one hundred acres of land. Today Arlington National Cemetery is one of the most prestigious burial grounds in the nation with fallen heroes from each of the country's wars, presidents, five-star generals, and the Tomb of the Unknowns. Just as they did during the Civil War, soldiers from adjoining Fort Myer (originally Fort Whipple) tend to the cemetery, today by providing Honor Guards and burial teams.

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All quotes from John G. Barnard's "Report on the Defenses of Washington
to the Chief of Engineers, U.S. Army." Published in Washington, D.C., 1871.  
1. Barnard,  33.
2. Barnard, 112.
3. Barnard, 112.
4. Barnard, 112.
5. Barnard, 117.