Afer Pope rushed into the safety of Washington, D.C., Lee decided to invade Maryland with the Army of Northern Virginia. As General Alexander wrote in his memoirs, “The enemy having taken refuge within lines impregnable to assault, Lee had no alternative but to take the offensive elsewhere. He could not afford to sit down before Washington and await the enemy’s pleasure.” E. Alexander, Military Memoirs of a Confederate, p. 220.

On September 4, 1862, the Army of Northern Virginia crossed the Potomac into the United States. Despite the victories of July and August, the Confederates lacked food and shoes. Alexander writes:

About one-half of the small-arms were still the old smooth-bore muskets of short range, and our rifled cannon ammunition was always inferior in quality. The lack of shoes was deplorable, and barefooted men with bleeding feet were no uncommon sight. Of clothing, our supply was so poor that it seemed no wonder the Marylanders held aloof from our shabby ranks. For rations, we were indebted mostly to the fields of roasting ears, and to the apple orchards.”

Memoirs, p. 223. Lee assigned D. H. Hill’s division – which included the 4th Georgia – to Stonewall Jackson’s wing of the army. Jackson led the way into Maryland.

But one of the great mistakes of the war threatened to destroy the Confederates. Lee decided to break his army into several parts – which might allow the Union army to overwhelm the widely separated commands. Lee sent Jackson back over the Potomac to capture Harper’s Ferry, a Union outpost in Virginia that threatened the Confederate offensive.

Lee moved the other wing under General James Longstreet to Boonsboro, Maryland, which lay on the west side of the South Mountain Range with the Union army on the East. D. H. Hill’s division formed the a rear guard at Turner’s Gap in the mountain chain.

But a Union private discovered a copy of Lee’s marching order at a Confederate campsite and relayed the document to General McClellan on September 13. Someone had wrapped the order around three cigars. “By all the maxims of strategy,” Alexander wrote, “Lee had put it in the power of McClellan to destroy [Lee’s] army.” p. 229.

In another twist, a Southern sympathizer “accidentally present” at Union headquarters when McClellan received Lee’s lost order overheard McClellan’s glee at the find. The sympathizer made his way through Union lines and told General J.E.B. Stuart after dark what had happened. Stuart informed Lee that night. Id. 230.

Lee moved to defend the mountain passes McClellan marched toward. McClellan moved carefully, although Lee had too few troops for successful defense. By September 14 – the day the gaps fell — Jackson had conquered Harper’s Ferry and begun his march to rejoin Lee. He headed for the town of Sharpsburg, on the Antietam Creek.

The 4th Georgia took part in the defense of Turner’s Gap. Other regiments did the fighting, however.

[I] with my command crossed over the Potomac River above Washington City with Gen’l Lee’s whole army. We camped at Fredericksburg, Maryland [actually Frederick], a few days and then went north to Boonsboro. I and my command witness’d the fighting at the Battle of Boonsboro Gap in the last of August 1862. We were stationed to guard a road on the mountain and did not fire a gun.”

Maryland held a 150th commemoration at the South Mountain Battlefields on September 14 and 15.