Following his raid on the B&amp;O railroad, central Maryland and aborted attack on Washington D.C. at the Battle of Fort Stevens, Confederate General Jubal A. Early retreated to Virginia, crossing the Potomac at Conrad's Ferry on July 14, making camp at Big Springs just north of Leesburg. On the 15th a detachment of Federal cavalry from Harpers Ferry led by General George Crook crossed into Loudoun from Berlin and skirmished with Confederates at Lovettsville. Early's Federal pursuers under General Horatio Wright reached Leesburg on the 16th and fought with Early's rearguard at Leesburg in the morning. Crook's cavalry skirmished with Confederate cavalry at Waterford later in the day. Late in the afternoon on the 16th, Federal cavalry under Alfred N. Duffié, also operating from Harpers Ferry, raided Early's wagon trains as they traveled west towards Snickers Gap on the Leesburg and Snickers Gap Turnpike just east of Purcellville at Heatons' Crossroads. That evening at dusk, Duffié's cavalry attacked and routed a detachment of Confederate cavalry in camp at Woodgrove. Early safely withdrew across the Blue Ridge on the 17th and established a line near Berryville in the Shenandoah Valley. The Union infantry under Wright drove off a small force of Confederates holding Snickers Gap in the afternoon of the 17th and were later attacked in camp by elements of Mosby's Rangers. The following day the pitched Battle of Cool Spring, or Snickers Ferry, was fought on its western slope as Union infantry tried unsuccessfully to force a crossing of the Shenandoah River. On the 19th, Mosby's Rangers engaged a detachment of Federal cavalry that was dispatched south to Ashby's Gap to conduct a flanking movement on Early's lines. The brief campaign was locally known as the Snickers Gap War.