After Confederate Gen. Jubal Early and his II Corps defeated Federal forces under Gen. David Hunter at Lynchburg on June 17-18, the Union army retreated into West Virginia, leaving the Shenandoah Valley – and its pathway north – in Early’s hands.
Early marched north down the Valley, side-stepped the Federal garrison at Harpers Ferry, and crossed the Potomac River at Shepherdstown into Maryland on July 5-6. On July 9, 1864, a makeshift Union force under Gen. Lew Wallace attempted to arrest Early’s invading Confederate divisions along the Monocacy River, just east of Frederick. Wallace, joined by Gen. James B. Ricketts’s Division of the VI Corps that had been rushed from the Petersburg lines, was outflanked by Gen. John B. Gordon’s Division and defeated after putting up a stiff resistance.
Hearing of Early’s incursion into Maryland, Union commander Gen. Ulysses S. Grant dispatched the rest of the VI Corps from Petersburg, sending them racing to Washington. Wallace’s defeat at Monocacy bought time for these veteran troops to arrive to bolster the defenses of the Union capital. Early’s advance reached the outskirts of Washington on the afternoon of July 11, and the remaining divisions of the VI Corps began disembarking that evening. Although Early advanced close enough to see the Capitol Dome through his field glasses, and there was some minor skirmishing and artillery fire (watched by President Abraham Lincoln himself), the timely arrival of the Union reinforcements eliminated the chances of a successful assault, and Early withdrew. Monocacy was called the “Battle that Saved Washington.”