Time and again, it was proven; the heights of Centreville were strategically significant during the sectional conflict of the Civil War. The ridge, on which Centreville is situated, held a strategic and commanding view of the panorama to the west. Approaches from the east were also within a viewshed visible from the ridge. Union Brigadier-General Irvin McDowell summed up the tremendous importance of holding the heights of Centreville:

For if he [the enemy] should once obtain possession of this ridge, which overlooks all the country to the west of the foot of the spurs of the Blue Ridge, we should have been irretrievably cut off and destroyed.[1]

Union Major-General Geo. B. McClellan, after reviewing the Confederate fortifications constructed in the winter of 1861/2, believed the position to be formidable.

From this it will be seen that the positions selected by the enemy at Centreville and Manassas were naturally very strong, with impassable streams, and broken ground, affording ample protection for their flanks, and that strong lines of intrenchments swept all the available approaches…That an assault of the enemy’s position in front of Washington, with the new troops composing the Army of the Potomac, during the winter of 1861-’62, would have resulted in defeat and demoralization, was too probable…[2]

The Centreville fortifications were used to cover the retreats of the Union army after both battles of First and Second Bull Run. Then, during the Bristoe Campaign, both armies rushed to achieve the heights of Centreville. Union troops were successful in seizing the position.

I shall to-morrow attempt to gain the heights of Centreville by crossing at the lower fords of Bull Run, and if I suceed, shall face Lee with my trains in my rear and await his further movements. - Geo. G. Meade, Major-General, Commanding.[3]

It is hoped we are sufficiently far ahead to enable the seizure of the Centreville Heights in advance of the enemy, but if the movement is detected our flank and rear may be attacked…General Newton, First Corps, will move from Bristoe through Manassas Junction,…thence to Centreville, by way of Mitchell’s Ford, seizing and holding the heights and redoubts. General Sedgwick…to the heights on the right of Centreville, looking toward Warrenton… The Reserve Artillery…to the rear of Centreville…Such additional batteries as may be required for the heights of Centreville will be placed in position… - S Williams, Assistant Adjunct General.[4]

General R.E. Lee considered attacking Union troops at Centreville in order to drive them back to their fortifications around Alexandria, but decided against the action.

I do not, however, think it advantageous to attack him in his entrenchments, nor do I see any benefit derived from pursuing him further…[5]

For the balance of the war, Union troops held Centreville as a crucial link in the chain of defenses surrounding and protecting Washington, D.C.

Confederate and Union armies, who alternated in occupying Centreville, each enhanced and expanded the earthworks left by the previous troops. It is difficult, based on imprecise descriptions, to ascertain with certainty which fortifications were constructed by which army.

The Confederates were first to construct some entrenchments at Centreville in 1861. Brig. Gen. Bonham took an advance position at Centreville in June 1861, but the Confederates retreated to Bull Run the following month when Union troops advanced on Centreville.[6]

No enemy appeared at Centreville…he having abandoned his intrenchments [sic] the night before…– I. B. Richardson, Colonel, Commanding Fourth Brigade, First Division [Union][7]

Union Brigadier-General Irvin McDowell, having become acquainted with the terrain, described the area as follows:

Centreville is a village of a few houses, mostly on the west side of a ridge running nearly north and south. The road from Centreville to Manassas Junction runs along this ridge, and crosses Bull Run about three miles from the former place. The Warrenton turnpike, which runs nearly east and west, goes over this ridge through the village, and crosses Bull Run about four miles from it, Bull Run having a course between the crossings from northwest to southeast…[8]

McDowell felt vulnerable to a flank attack, should the enemy cross Bull Run at Blackburn’s Ford and advance to Centreville along the ridge, and ordered an engineer to extemporize some field works to strengthen the position.[9]  In July 1861, Union troops began to enhance and extend the existing Confederate works, and to construct new entrenchments. Under the direction of First Lieutenant Frederick E. Prime, an engineer officer, at least four strategic positions were fortified.

Blenker’s brigade took position at Centreville, and commenced throwing up intrenchments – one regiment being located at the former work of the enemy, one to the west of the town on the Warrenton road, and two on the heights towards Bull Run… - D. S. Miles, Colonel Second Infantry, Commanding Fifth Division [Union][10]

Colonel Miles, on whose staff Prime was attached, examined a battery on the road from Fairfax Court-House; after which, the pioneers of the Garibaldi Guard were ordered to construct a redoubt with two embrasures, so as to sweep the old Braddock road so that Confederate troops could not outflank them from Union Mills Road or the road from Gaines’ Ford.[11] Further orders to defend against a flank attack stipulated the positions to the east of Centreville.

…the brigade advanced from the camp and took up their assigned position on the heights of Centreville east of Centreville about daybreak: the Eighth Regiment New York State volunteers…on the left of the road leading from Centreville to Fairfax court House; the Twenty-ninth Regiment New York State Volunteers…on the right of the same road, both fronting towards the east; The Garibaldi Guard…formed a right angle with the Twenty-ninth Regiment, fronting on the south…three pieces left in Centreville were placed near the right wing of the Twenty-ninth Regiment; three others on the left wing of the Eighth Regiment, where intrenchments were thrown up by the pioneers attached to the brigade…[12]

Late in the evening of October 16, 1861, General Joseph Eggleston Johnston’s army arrived in Centreville and soon began construction of forts, breastworks, riflepits, and batteries on the high ground and at strategic locations. A sketch map drawn in December of 1861 depicts the location of the fortifications and troop encampments.

George Wise, of the Seventeenth Virginia Infantry, recollected the construction of fortifications by the Confederates.

…the Army of Northern Virginia soon made Centreville what Fairfax Courthouse had been and the fields around were converted into drill grounds for thousands of Confederate soldiers. Engineers were soon at work; forts, breastworks, rifle pits and batteries, marked the high points around. Regular details from every regiment in the army were daily made for ditching and digging, and the adjacent country for miles around became alive with men. The big balloon of the enemy appeared often in the direction of the Courthouse, and, no doubt, its occupants took the Southern army for a large body of sappers and miners, as men and officers for days and weeks were in the [ditch].[13]

On March 14, 1862, Lieutenant McAlester, U. S. Engineers, surveyed and described the recently deserted Confederate fortifications at Centreville.

Private Robert Knox Sneden wrote in his diary on August 30, 1862, during the second Battle of Bull Run, that Union troops were establishing new defenses at the old forts at Centreville.

Lanterns were seen moving all night on the old Rebel forts at Centreville, while the sound of hundreds of axes were heard on all sides. Our engineers were putting Centreville in a state of defense, pulling down houses and mounting guns.[15]