William Swinton, Campaigns of the Army of the Potomac

Three out of the six corps of the Army of the Potomac, and they the strongest, had thus been drawn into the seething vortex of action on the right; and each in succession, while exacting heavy damage of the enemy, had been so punished as to lose all offensive energy; so that noon found them simply holding their own. Porter with his small reserve corps, numbering some fifteen thousand men, held the centre, while Burnside remained inactive on the left, not having yet passed the Antietam.¹ Now, between twelve and one o'clock, Franklin with two divisions of his corps, under Slocum and W. F. Smith (Couch remaining behind to occupy Maryland Heights), reached the field of battle, from where the action at Crampton's Pass had left him. General McClellan had designed retaining Franklin on the east side of the Antietam, to operate on either flank or on the centre, as circumstances might require. But by the time he neared the field, the strong opposition developed by the attacks of Hooker and Sumner rendered it necessary for him to be immediately pushed over the creek to the assistance of the right.² The arrival of Franklin was opportune, for Lee had now accumulated so heavily on his left, and the repulse of Sumner's right under Sedgwick had been so easily effected, that the enemy began to show a disposition to resume the offensive— directing his efforts against that still loose-jointed portion of Sumner's harness, between his right and centre. General