After Confederate Gen. Robert E. Lee's victory at Chancellorsville in May 1863, he led the Army of Northern Virginia west to the Shenandoah Valley, then north through central Maryland and into Pennsylvania, while Union Gen. Joseph Hooker's Army of the Potomac marched into northern Virginia in response. On June 18, Union Gen. Henry W. Slocum's XII Corps arrived in Leesburg, and the next day Slocum requested a bridge over the Potomac River at Edwards Ferry so supplies could be drawn from the Chesapeake and Ohio Canal on the Maryland side and avoid Confederate irregulars in Loudoun County. Hooker approved the request, and Federal engineers completed the first pontoon bridge on June 21, with a landing upstream from the mouth of Goose Creek on the northern bank, then soon added a span across Goose Creek near its mouth. After Lee's army entered Pennsylvania, Hooker chose Edwards Ferry for a rapid crossing of the Potomac; engineers placed a second bridge on June 25 with a landing downstream from the mouth of Goose Creek, and beginning that morning the army crossed. Over three days, nearly 80,000 infantrymen, 12,000 cavalrymen, 370 artillery pieces, and 3,000 supply wagons, in a column estimated at 80 miles long, passed over the Potomac at Edwards Ferry, and most of the Federal force that fought at Gettysburg crossed there. George Kephart had purchased a mill on Goose Creek in 1841, on the partially completed Goose Creek Canal, and a bridge once spanned the creek there, but Confederates burned it early in 1862 and its stone abutments still stand.