This stream pours into the Potomac just above, from the Maryland side. It gives its name to one of the most interesting actions of the war. The fields of Antietam and Gettysburg were the only two great battle grounds on which the Confederates played the rôle of invaders and left the protection of their native States. Antietam was the first, and if it could have been made for Lee a more decisive failure, might have prevented Gettysburg. It occurred September 15th to 18th, 1862. Lee had just thoroughly whipped that handsome Western braggart, General Pope, and, elated with success, thought he could assume the offensive, cross the Potomac, and collect around his banner great armies of dissatisfied secessionists to the tune of "Maryland, my Maryland." McClellan (then in the last month of his command over the army of the Potomac) pushed with unwonted vigor over the mountains, inspired, it is said, by the accidental foreknowledge of Lee's whole Maryland plan, and clashed with Lee across the bridges of this pretty highland stream. As an episode he lost Harper's Ferry; but that was a trifle. It was a murderous duel, that which raged around the Dunker church and over the road leading from Sharpsburg to Hagerstown. Lee's forty thousand men were shielded by an elbow of the Potomac; his batteries of horse-artillery under Stuart were murdering the forces of Hooker, when that general was relieved by the support of Mansfield; then Mansfield was killed and Hooker wounded; and then Sedgwick was sent up to replace Mansfield; then, when Sedgwick was getting the better of Jackson and Hood, McLaws and Walker drew up to the Confederate left, and burst completely through Sedgwick's line. Presently, Franklin and Smith came across from the stream and reinforced the Federals, driving the Southern advance back to the church, and Burnside rendered some hesitating assistance; but then rushed up the force which had received the surrender of Harper's Ferry, singing victory, and drove back Burnside; and when McClellan, on the morning of the 19th, found that Lee had withdrawn across the Potomac, he was too much discouraged with his own hurts to venture a pursuit. He had lost twelve thousand men, and Lee eight thousand. But Antietam, though for us a costly and unsatisfactory victory, was for the South a conclusive lesson. The Peter-the-Hermit excursion into Maryland lasted just two weeks, and its failure was signal and instructive. Intended as an invasion that should result in the occupation of Washington and Philadelphia, it led to nothing but to Stuart's audacious raid into Pennsylvania with his thousand troopers--a theatrical flourish to wind up an unsuccessful drama. As for Harper's Ferry, its overwhelming punishment and precipitate conquest were not without their use: the retention by the Federals of the little depot of army stores on the Virginia bank surprised and thwarted Lee. To reduce it, he had to pause, and ere the