Maj. Jed. Hotchkiss, Confederate Military History, a library of Confederate States Military History: Volume 3, Virginia
Clement Anselm Evans, Ed.

The first State troops to reach Washington after Lincoln's call was the Sixth Massachusetts, which was attacked in passing through the streets of Baltimore, on the 19th of April, by unorganized citizens, but reached Washington late that day and was encamped in the capitol. After the passage of these troops, the railways from Baltimore north to Harrisburg and east to Philadelphia were broken in consequence of the destruction of bridges by Southern sympathizers, and were not again opened for travel until the 7th of May; but in the meantime, troops in large numbers were brought to Washington from the North and the West by steamers from Perryville, on the Susquehanna, on the road to Philadelphia, down the bay to Annapolis, and thence by rail across to Washington, and also around the coast to Chesapeake bay, and up that and the Potomac, so that quite an army was gathered in that city when Col. J. K. Mansfield took command of it on the 27th of April. Steps were taken to guard the bridges from Virginia and all other approaches, Lincoln on the same day calling for twenty-five regiments of regulars in addition to the 75,000 three-months' men previously called.

On the 25th of April, the Confederates planted batteries on Arlington heights, and placed guards in Alexandria and along the Potomac above and below Washington. On the 28th, Federal troops guarded the northern, and Confederate troops the southern, end of the long bridge; but on the 30th, General Lee ordered the withdrawal of all troops between the long bridge and Alexandria, to avoid provoking a collision for which he was unprepared. On the 5th of May, the Confederate forces in Alexandria, some 500 in number, including 70 cavalry, under Lieut.-Col. A. S. Taylor, alarmed by a rumored attack, evacuated Alexandria, without orders, and fell back to Springfield. General Cocke, in command along the Potomac, from his headquarters at Culpeper promptly ordered them back. On the 9th two Virginia regiments of infantry were ordered to Cocke, and on that day he located his headquarters at Manassas Junction and began the gathering of troops at that point, establishing connections with Col. Daniel Ruggles, in command at Fredericksburg with his advance at Aquia creek on the Potomac,