He had but 45,000 men with whom to undertake a task for which a quarter of a million would not have been an excessive or even a certainly sufficient force. But those 45,000 men were soldiers of the very best quality imaginable. They had been seasoned by severe campaigning. They had accustomed themselves to win in battle against heavy odds. They believed in their leader and in themselves and were ready to undertake any task that Lee might assign them. They were stubborn men and stalwart, and experience on march and in battle had made them as nearly perfect soldiers as the world has anywhere or at any time known. On such an expedition as that which Lee planned, they were certain to be opposed by armies greatly exceeding themselves in numbers and immeasurably superior in equipment and supplies. But they were soldiers of that sort that can march on a diet of hard tack and fight on no diet at all. So with this slender force Lee crossed the Potomac, on the fifth of September, abandoning his base of supplies and his communications and depending for the support of his army upon such foodstuffs as he could secure in his enemy's country. As for reinforcements, he perfectly knew that there were none who could come to him. It was a desperate hazard, conspicuously Napoleonic in its daring. Crossing the Potomac on the fifth of September, Lee established himself on the eighth near Frederick, Maryland, a point at which his presence threatened Washington and Baltimore about equally. And both those cities must be guarded against his advance, the direction of which was of course uncertain. The capture of either city would mean the speedy surrender of the other. To meet this danger the Federal Administration hurriedly called to Washington every regiment and brigade it could in any wise command. It united the armies of McClellan and Pope and reinforced them with every regiment that could be drawn from other quarters. It restored McClellan to command--for he had been temporarily removed in consequence of his disastrous defeat at Richmond--and set him the task of defending the National capital by meeting and crushing Lee in the field. If Lee had commanded an army of half a million men instead of the meager 45,000 actually under his orders, the alarm could scarcely have been greater or the preparations to meet him more elaborate. President Lincoln visited McClellan in person and asked him to resume command of the combined armies. McClellan accepted the commission.