The Fortification System

Interior view of Fort in Washington DC
Interior view of a Civil War fort in Washington, DC, including Federal soldiers posing near artillery pieces. The image is often identified as Fort Totten, built as part of the Northern Defenses in Fall 1861.

Library of Congress

During the Civil War, the U.S. Army constructed an elaborate system of fortifications to protect the capital. By war's end, Washington D.C. was one of the most heavily fortified cities in the world.

According to General John G. Barnard, Chief Engineer of the Defenses of Washington, the protection of the capital began "from a few isolated works covering bridges or commanding a few especially important points, [and] was developed a connected 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 which were in fact lines of infantry parapet, furnishing emplacement for two ranks of men and affording covered communication along the line, while roads were opened wherever necessary, so that troops and artillery could be moved rapidly from one point of the immense periphery to another, or under cover, from point to point along the line."

The number of forts, guns or other aspects of the fortifications were not necessarily important; the combination of the forts, batteries, blockhouses, trenches and guns and their interaction made the entire fortification system effective.

The Forts

General Barnard declared that the general profiles, or sections, of the works were derived from those in Dennis Hart Mahan's A Treatise on Field Fortifications. Mahan, professor at the United States Military Academy at West Point, 1824-1871, was revered by multiple generations of future career army officers, including Barnard and Major General George B. McClellan. Generally, the Army Engineers planned the forts for approximately a 500-man garrison and for about 16 guns. "In the construction of these works the heights of the interior crest of the parapet was from 7 to 9 feet above the parade; the thickness of the parapet ranged from 12 to 18 feet; the ditches were usually 6 feet deep, and a few feet beyond the counterscarp a glacis was constructed upon which an abattis was placed; revetments of plank, vertical posts, fascines or sod were used, the cheeks of embrasures being revetted with gabions."

An Army Engineer publication on "The Art of Fortification," described the forts this way:

"The profile of these forts consisted of an earthen parapet from 12 to 18 feet thick (the thickness depending upon exposure). The interior slope was revetted while the exterior slope was allowed to take the natural slope of the earth. At the foot of the exterior slope proper, there was a narrow berm, outside of which there was a ditch at least 6 feet in depth. Outside of the ditch the ground was graded so as to form a glacis with a narrow covered way fitted occasionally as an infantry parapet. On the glacis or at its foot there was usually built an abatis. When first constructed, the interior slope was revetted with planks, but these proved to have so little durability, they were later replaced by a revetment consisting of vertical posts, capped by horizontal logs which were well tied back into the parapet.

Within the forts, bombproof magazines and bombproof quarters were plentifully supplied and the earth covers of these were frequently fitted as infantry parapets."

The Batteries

The Army Engineers also constructed numerous batteries between the forts. Major General George B. McClellan wrote: " The intermediate points [between the forts] were occupied by lunettes, redoubts, batteries, etc., and in a few cases these were united by infantry parapets. The entire circumference of the city was thus protected. " The Commission that studied the fortifications in late 1862, after examining and reporting on each fortification, recommended the construction of "numerous batteries . . . in the intervals between the forts." By constructing these batteries, the intervening space between the forts was also covered by artillery fire. Not all the batteries received guns; various authors report that over ninety batteries were not armed.

In his post-war report, published in 1871, Barnard described the batteries:

The Blockhouses

During the Civil War, the U.S. Army erected numerous wooden blockhouses to protect railroad lines, bridges, roads, and important defiles. Likewise, the Army erected blockhouses in the defenses of Washington, D.C. The Army designated three of these blockhouses by numbers: Blockhouse No. 1 and Blockhouse No. 2 were located near Hunting Creek Valley, one at the north side of the valley at the Little River Turnpike and one on Telegraph Road near the bridge over Hunting Creek, and Blockhouse No. 3 on the Leesburg Turnpike near Fort Ward.

The Trenches and Rifle Pits

The Defenses of Washington, the main forts, were fully connected by earthen trenches and rifle pits. According to General Barnard, "In addition to the forts proper, there were between the forts [and batteries], and forming as it were the curtains, some 20 miles [approximately 35,711 yards] of rifle trenches . . ."The whole line was connected by rifle-trenches which were in fact lines of infantry parapet, furnishing emplacement for two ranks of men and affording covered communication along the line . . ."

Barnard described the trenches in detail:

"TRENCHES AND COVERED WAYS".–The connecting lines, destitute of interior revetments, had, in place, thereof, earth slopes of about 45 degrees. The earth was thrown up from an inside excavation, which was carried to sufficient depth (usually 3 feet) to afford, in conjunction with the embankment, a cover of 71/2 feet. The banquette was made on the natural surface of the ground. To facilitate access from the trench an intermediate step, 2 feet in width, broke the continuity of the earth slope. The bottom of the trench was graded to throw the drainage to the rear, and outlets for it were provided at suitable localities. For the uses of infantry alone a width of 5 feet was given to the bottom of the trench, from which resulted a thickness, between crests, of parapet of 4 feet. Wherever it was considered desirable to provide for the passage of guns these dimensions were increased to 8 feet for both trench and parapet. Sometimes such trenches were adapted to the service of guns, in which cases platforms of well-compacted earth were made, and on each side of the embrasure the parapet was revetted, either with wall-sodding or posts. The embrasures were revetted either with gabions or with sods. The full width of trench was cut to the rear of the platforms, with easy ramps for crossing them and for running the guns into position. When the second form of trench was used to connect a fort with a contiguous battery the interior slope was usually revetted with posts, instead of being of earth at its natural slope."

The Water Defense

Both Fort Foote (Fort Washington, Maryland) and Battery Rodgers (Jones Point Park in Alexandria, Virginia) anchored the defenses on the Potomac Rivers' southern approach and were often referred to as water or river or shore batteries. No enemy forces attempted to ascend the river for an attack on Washington so it is difficult to assess the value of these fortifications. At the end of the war, the Army had numerous proposals for the post-war use of the fort and battery. The Army did not retain Battery Rodgers but it did keep Fort Foote, which in association with Fort Washington was to repel invasions and raids up the river. The Army Engineers remodeled and enlarged Fort Foote during its use but stopped using it as a water defense in 1874. The site was abandoned in 1877, but was reactivated for a short period during the Spanish American War.

Additionally, the Army Engineers constructed obstructions that could be moored in the Potomac River, near Fort Foote, and "render the shore batteries [Fort Foote and Battery Rodgers] more efficient for the protection of Washington against maritime attack." In July 1864, Congress appropriated $300,000.00 for the fabrication of the obstructions and Lt. Colonel Barton S. Alexander, who succeeded General Barnard as Chief Engineer,, designed "a series of floats holding up a 400-foot-long chain with 23 anchors . . ." that some referred to as the "Alexandria Chain," but they were unused during the war. After the war, the Army held on to the obstructions and, in 1868, offered them to the Secretary of the Navy who, it turned out, considered them worthless. The obstructions remained stored in a shed near Fort Foote, deteriorating, at least into the early 1870s.

The Roads

To facilitate the movement of men and supplies, the Union army constructed a system of military roads that encircled city.

In his 1871 report on the defenses of Washington, Barnard described the roads as such:

"MILITARY ROADS.–The line of defensive works was readily reached by the several county roads radiating from the cities of Washington, Georgetown, and Alexandria; but there existed, at first, no adequate means of communication along any portion of the line, and none at all along some portions of it. The necessity for such communicating roads became apparent as soon as the general line of works was established. The conditions governing their location and construction were, that they should not be seen from any ground that an enemy might be able to occupy in front, that they should be as direct as practicable consistently with easy grades, and that they should have sufficient width for the movement over them of field batteries or army trains."

Later in the same report, Barnard stated: "The aggregate length of military roads constructed was about 32 miles. Providing, as they did, the means of rapidly moving troops or guns, unobserved by the enemy to reinforce any part of the line that might be attacked, their importance as adding to the strength of the defensive system can scarcely be over-estimated."

The Bridges

Almost as important as the roads for movement of supplies, equipment and materiel were the bridges. The only three bridges across the Potomac were Long Bridge, Aqueduct Bridge and Chain Bridge until 1864 when a railroad bridge was added, next to Long Bridge. The Navy Yard Bridge and Benning's Bridge crossed the Anacostia River, or as some called it the Eastern Branch. Fortifications and a guard unit protected all of these bridges. In addition, bridges on various roads crossed lesser streams and creeks. All the bridges required maintenance and in most instances, improvements. Without the bridges, the roads would not have been of much use.

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Last updated: August 27, 2020

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