John G. Nicolay, The Outbreak of Rebellion

[110] already had a detachment quartered at Alexandria; reinforcements from the South might, in a single night, occupy the heights and destroy the Virginia end of the bridges, and, speedily erecting mortar batteries, could destroy the city with bombs, unless they were attacked at a disadvantage and dislodged. It was, therefore, decided that the Union forces must occupy Arlington Heights to insure the safety of the city, though the necessary troops could not as yet be spared from the operations to secure Maryland; and by reason of various delays, three weeks more passed away before the full preparations for the enterprise were completed.

Finally, at two o'clock on the morning of May 24th, three columns crossed the Potomac and entered on the “sacred soil” of the Old Dominion: three regiments by the Aqueduct at Georgetown, four regiments by the Long Bridge from Washington, and one regiment, Ellsworth's Zouaves, from their camp below the city directly by steamer to Alexandria, the war steamer Pawnee being anchored off shore to protect the landing. The movement met no opposition; no considerable rebel force was stationed at the bridges, and the detachment at Alexandria, excepting a small troop of cavalry, which was captured, evacuated that place on receiving a notice, sent without authority by the commander of the Pawnee, to surrender or retire.

It had been a beautiful moonlight night; all the regiments were filled with an eager enthusiasm for the march; the preparations were careful, the officers to supervise it intelligent and competent, the movements promptly begun and successfully completed. The whole enterprise seemed on the very point of conclusion without an accident, when sudden news of the assassination of Colonel Ellsworth not only saddened the camps on both sides of the Potomac, but