From the time of Virginia's secession from the Union on May 23, 1861, until just before the Battle of Manassas on July 21, 1861, the Confederate government in Richmond recognized the importance of defending the Lower Shenandoah Valley. When Confederate General Joseph E. Johnston occupied Winchester in June, 1861, he began to fortify the town with earthworks. Fort Collier was probably built under the supervision of General W.H.C. Whiting, Johnston's chief engineer.
In the first months of the Civil War, soldiers were reluctant to engage in the backbreaking work essential to build prepared artillery and infantry entrenchments. That soon changed. By the spring of 1862, Virginia was the most heavily fortified state in the Confederacy. Earthworks protected the Confederate positions at Manssas and also along the Virginia Peninsula. After General Robert E. Lee Replaced Johnston in command of Confederate forces in Virginia, on June 1, he began the construction of earthworks around Richmond. By that time, Fort Collier had been completed as an earthwork fortification, commanding the approach to Winchester along the Martinsburg Pike. Collier had sited the fort to bring converging fields of artillery and rife fire on any Federal advance, maximizing Confederate firepower while protecting the garrison behind the parapet.
Fort collier did not figure in either the First (1862) or the Second (1863 Battles of Winchester. In 1864, however, Fort Collier's importance became clear. After the Second Battle of Kernstown (1864), Lieutenant General Jubal A. Early used Winchester as a base against larger Federal forces throughout his daring war of maneuver in August and early September. On September 19, his opponent, Major General Philip Sheridan, suddenly advanced on Winchester from the east, along the lightly fortified Berryville Pike, beginning the Third Battle of Winchester. By late that afternoon, with the outnumbered Confederates pressed back almost into Winchester, Fort Collier had become the anchor of Early's left and the key to the battle. Exactly how many infantrymen and artillery pieces were in the fort at the time is unclear. Certainly the small force would be no match for the great cavalry charge—the largest in American history—that swept up the Martinsburg Pike, overcame Fort Collier, and ended the Third Battle of Winchester.