Just one week after the Second Battle of Bull Run, Gen. Robert E. Lee decided it was time to take the war into the North. By marching his victorious army into Maryland, Lee had several objectives. First, he wanted to maintain the momentum achieved with his stunning victory at Bull Run a few days earlier, which left the retreating Union army in chaos. By marching into Maryland, Lee could relieve Virginia of enemy occupation. He knew the Union army would have to mirror his movements and take up defensive positions in front of Washington and Baltimore.

Logistically, also, moving his army into the unharvested, virgin countryside of western Maryland would provide new food supplies for Lee's hungry soldiers, and the merchant stores in Frederick could resupply his troops with new clothing and shoes. Also September and October mark the key harvest months. Without Union armies to bother them, the Southern farmers could gather their harvests and be able to feed Lee's armies during the upcoming winter.

Lee also hoped that by his moving into Maryland the undecided border state would join the Southern cause. Possibly he could influence the upcoming Congressional Elections and cause more Democrats--who favored peace--to be able to outvote the Republican majority in the House and demand an end to the war.

However, as a larger objective Lee hoped that a victory in the North by his extremely confident army could gain diplomatic recognition from Europe and possibly bring England and France to the aid of the South. Such a victory might cause the people of the North to question President Lincoln's leadership and force him to sue for peace.

And so on Thursday morning, September 4, 1862, the dirty, ragged Army of Northern Virginia splashed across the shallow fords of the Potomac River just north of Leesburg to the strains of "Maryland, My Maryland." By midmorning, Saturday, September 6, Gen. "Stonewall" Jackson's advance force of 5,000 men marched down Market Street in Frederick and made camp on the north side of town. The remainder of Lee's 40,000-man army soon followed.

Upon his arrival in town, Lee drew up a Proclamation to the People of Maryland, inviting them to side with the Southern movement. For the next several days Lee's troops, upon strict orders not to pillage, bought food and all the shoes and clothing they could find at the stores in town. But soon it became obvious that the citizens of Frederick, though polite, had no sympathy for the Southern cause.

So Lee drew up a new set of plans. He would divide his forces into four sections, sending Gen. Jackson with six divisions of 22,000 men to eliminate the 12,000-strong Federal garrison at Harpers Ferry to the southwest. The remaining three divisions of Lee's forces--18,000 men, under Gen. James Longstreet--would move northwest over the Catoctin and South Mountain ranges to Boonsboro and Hagerstown, a distance of 25 miles.

Later Jackson would rejoin Lee and Longstreet at Hagerstown. Then, using these mountain ranges to protect his right flank, Lee could move his combined Confederate forces northeast along the rail line to Harrisburg, the capital of Pennyslvania and a key rail center for the Union. Early on Wednesday morning, September 10, Lee's forces began leaving Frederick to carry out their assignments.

Three unforseen events, however, would disrupt Lee's plans. Gen. George McClellan would reorganize the Army of the Potomac in days, rather than weeks as Lee expected, and arrive in Frederick on Friday, September 12th. Second, the garrison at Harpers Ferry, rather than fleeing, was ordered to stand until reinforcements could arrive. Third, an official copy of Lee's Special Order 191--wrapped around three cigars--would be found by a Union private in an abandoned Confederate campsite the next day.

When Lee learned that McClellan's army was moving westward from Frederick, he realized the peril in which his divided forces found themselves. Quickly he sent troops to block the three main passes over South Mountain, providing sufficient time to concentrate the majority of his forces in a defensive position around Sharpsburg, six miles to the southwest of Boonsboro. At the same time McClellan, with 85,000 men, gathered on the east bank of the Antietam Creek. And thus, late on September 16, all the pieces were in place late for the battle that would begin at sunrise the next morning--the battle that would become the bloodiest day of the Civil War.