Harpers Ferry is a small town at the confluence of the Potomac River and the Shenandoah River, the site of a historic Federal arsenal founded by President George Washington in 1799 and a bridge for the critical Baltimore and Ohio Railroad across the Potomac. In 1859 it was the site of the abolitionist John Brown's attack on the Federal arsenal.

The town was virtually indefensible, dominated on all sides by higher ground. To the west, the ground rose gradually for about a mile and a half to Bolivar Heights, a plateau 668 feet high, that stretches from the Potomac to the Shenandoah. To the south, across the Shenandoah, Loudoun Heights overlooks from 1,180 feet. And to the northeast, across the Potomac, the southernmost extremity of Elk Ridge forms the 1,476-foot-high crest of Maryland Heights. A Federal soldier wrote that if these three heights could not be held, Harpers Ferry would be "no more defensible than a well bottom."

The Civil War was disastrous for Harpers Ferry, which changed hands eight times between 1861 and 1865. Because of the town's strategic location on the railroad and at the northern end of the Shenandoah Valley, both Union and Confederate troops moved through Harpers Ferry frequently. The town's garrison of 14,000 Federal troops played a key role in the Confederate invasion of Maryland in September 1862. Gen. Robert E. Lee did not want to continue on to Maryland without capturing the town. It was on his supply line and could control one of his possible routes of retreat if the invasion did not go well.