The Chain Bridge Defenses During the Maryland Campaign, Part II: Sigel Adjusts His Line While the Confederates Demonstrate at Pimmit Run

Last week I examined the withdrawal of John Pope's defeated Union force following Second Manassas.  Franz Sigel's First Corps of the Army of Virginia, along with the corps of Edwin V. Sumner and Fitz John Porter, moved from Fairfax Court House to Langley.  By September 3, 1862, Sigel's men occupied the ground closest to the strategic crossing at Chain Bridge.  Porter sat not far away, around Hall's Hill, while Sumner crossed the Potomac and took up a position at Tennallytown.

As Gen. George B. McClellan divined Robert E. Lee's next move, he sent instructions through his chief of staff, Randolph B. Marcy, to ensure the adequate safeguarding of Washington's defenses.  On the morning of September 4, Sigel was told to "draw in the main line of his forces. . . so as to run from Ft. Ethan Allen toward [Porter's] right."  (OR, 1:51:1, 789.)  This shift would shorten Sigel's line and close any gaps between the two corps.  (OR, 1:51:1, 785, 789.)  

That same day, a small fight erupted about a half a dozen miles from Sigel's force near Chain Bridge.  As Lee prepared his army to invade Maryland by crossing the Potomac near Leesburg, Confederate cavalry was ordered to make a demonstration in front of the Federal lines near Washington.  On the morning of September 4,  Gen. Beverly Robertson led the 7th and 12th Virginia Cavalry and three guns from Capt. R. Preston Chew's horse artillery down the Leesburg-Alexandria Turnpike towards Falls Church.  Between Vienna and Lewinsville, the Confederates ran into Union pickets from Gen. Alfred Pleasonton's cavalry command and drove them back "after a brisk skirmish."  (OR, 1:19:1, 828.)  Robertson sent one gun and part of his cavalry to a point "near Lewinsville to prevent surprise" and proceeded with the rest of his force to a hill above Pimmit Run along the pike.  (OR, 1:19:1, 828; see also OR, 1:19:2, 176.)*  Two of Chew's guns opened on the Union troops, and the Federals soon returned fire with two guns of their own.  Around six that evening, Marcy alerted Sigel to the attack and cautioned him:

Your pickets should be on the alert, and your command at once drawn into the new position indicated to you this morning.  (OR, 1:51:1, 785.) 

Robertson's fight with the Union troops lasted until about sundown, when the Confederates spotted several regiments advancing from the direction of Falls Church.  Robertson deemed "the object of the reconnaissance. . . fully accomplished" and withdrew his men "at dark."  (OR, 1:19:1, 828; see also OR, 1:19:1, 814; OR, 1:19:2, 176-78; Harsh 67.)  Pleasonton dismissed the action as a mere "show of force to conceal [Lee's] movements on the Upper Potomac," and McClellan agreed.  (OR, 1:19:2, 178; OR, 1:51:1, 785.)

Gen. Beverly Robertson (courtesy of Wikipedia).  The cavalry commander had few fans among the top brass of the Army of Northern Virginia and was transferred to North Carolina soon after the skirmish of September 4.

Armed with intelligence on Lee's intentions, McClellan set his army in motion to pursue the Confederates in Maryland.  His entire force, however, would not go with him.  The Lincoln Administration wanted assurances that Washington would remain sufficiently protected.  For the time being, Sigel's corps would have the chief responsibility for guarding the key approaches to Chain Bridge. 

Late on the afternoon of September 6, Marcy sent an order to Sigel at Ft. Ethan Allen:

The commanding general directs that you at once place your corps in position to occupy the line extending from Forts Marcy and Ethan Allen to the vicinity of Fort De Kalb. General F. J. Porter's corps will occupy the line from Fort De Kalb to Hunting Creek, and General [Samuel P.] Heintzelman the line from Hunting Creek to the river below Fort Lyon. . . .  You will please post your pickets well out so as to give timely information of the approach of the enemy.** (OR, 1:51:793.)

Marcy emphasized in a postscript: "Forts Marcy and Ethan Allen will be intrusted to your charge, and you will please connect your pickets with those of General Porter."  (OR, 1:51:1, 793.)  The admonishment about tightening the line likely stemmed from complaints by Porter, who a few days earlier had advised Marcy to send "a staff officer along our lines, to establish the picket lines and the proper connections between corps."  (OR, 1:19:2, 179.)  Not long after Marcy sent the order to Sigel, he reassured Porter that "General Sigel will hold the forts at the Chain Bridge and connect with you."  (OR, 1:51:1, 791.)

Detail from 1862 Union Army map of Northeastern Virginia showing the area of Sigel's line from Ft. Marcy and Ft. Ethan Allen near Chain Bridge to the vicinity of Ft. DeKalb (courtesy of Library of Congress).  For a modern view of the same area, see here.

That night, the area around Chain Bridge buzzed with activity.  McClellan ordered the Sixth Corps under Gen. William B. Franklin to cross the bridge and march to Rockville via Tennallytown.  (OR, 1:51:1, 793; OR, 1:19:1, 38.).   Gen. George Sykes's division from Porter's corps was likewise instructed to proceed to Tennallytown.  (OR, 1:51:1, 791; OR, 1:19:1, 38.)  As the day dawned on September 7, the bulk of McClellan's army sat across the Potomac from Virginia.  Little Mac was on the move, and Sigel's men may have started to wonder when their turn would come.

Notes

*This fight likely occurred near the current-day location of the Whole Foods supermarket along Leesburg Pike (Rt. 7)  (See here for a map). 

**Ft. Marcy and Ft. Ethan Allen guarded the immediate approaches to Chain Bridge on the Virginia side of the Potomac above Georgetown.  For more on the two forts, see here and here.  Ft. DeKalb sat near current-day US-29 (Lee Highway) between N. Adams and N. Vance Streets in Arlington, Virginia.  It was later renamed Ft. Strong.  Hunting Creek is a tributary stream of the Potomac located to the south of Alexandria, Virginia near the present-day Woodrow Wilson Bridge.   Ft. Lyon was located beyond Hunting Creek to the southwest of Alexandria.  For a complete map of the defenses of Washington from the OR, see here.

Sources

Aside from the citations to the Official Records above, the following sources were useful in compiling this post:

Samuel P. Bates, History of Pennsylvania Volunteers, 1861-1865, Vol. I (1869); Benjamin Franklin Cooling III & Walton H. Owen II, Mr. Lincoln's Forts: A Guide to the Civil War Defenses of Washington (2010 ed.); Stephen D. Engle, Yankee Dutchman: The Life of Franz Sigel (1993); Bradley Gottfried, The Maps of Antietam (2012); Joseph L. Harsh, Taken at the Flood: Robert E. Lee & Confederate Strategy in the Maryland Campaign of 1862 (1999); George Michael Neese, Three Years in the Confederate Horse Artillery (1911); Stephen W. Sears, Landscape Turned Red: The Battle of Antietam (1983).