McClellan was in his element in fusing into unity the disjointed fragments of armies which lay about in Virginia like scattered ruins. His bitterest tractors have never denied him the gift of organization, and admit that he did excellent service just now for a few days. But circumstances soon extended his field of action, and gave detraction fresh opportunities. General Lee, in a bold and enterprising mood, perhaps attributable to the encouraging inefficiency of his Northern opponents, moved up the banks of the Potomac and threatened an irruption into Maryland and even Pennsylvania. It was absolutely necessary to watch and, at the right moment, to fight him. For this purpose McClellan was ordered to move along the north bank of the river, but under strict injunctions at first to go slowly and cautiously and not to uncover Washington. For General Halleck had not fully recovered his nerve, and was still much disquieted, especially concerning the capital. Thus the armies drew slowly near each other, McClellan creeping forward, as he had been bidden, while Lee, with his usual energy, seemed able to do with a thousand men more than any Northern general could do with thrice as many, and ran with exasperating impunity those audacious risks which, where they cannot be attributed to ignorance on the part of a commander, indicate contempt for his opponent. This feeling, if he had it, must have received agreeable corroboration from the clumsy way in which the Federals just at this time lost Harper's Ferry, with General Miles's garrison. The Southern troops, who had been detailed against it, rapidly rejoined General Lee's army; and again the people saw that the South had outmarched and outgeneraled the North. With all his troops together, Lee was now ready to fight at the convenience or the pleasure of McClellan, who seemed chivalrously to have deferred his attack until his opponent should be prepared for it! The armies were in presence of each other near where the Antietam empties into the Potomac, and here, September 17, the bloody conflict took place.