The advance was made most gallantly, the enemy utterly routed, and the heights carried triumphantly. Night was now approaching, and the enemy was receiving strong reinforcements from Harper’s Ferry. General Burnside’s troops were attacked on the left flank, and obliged to retire to a lower line of hills, near the bridge and the question as to whether the well-won position on the heights could be maintained, became a problem of vital importance. Burnside’s brigades were in close columns, and would not give way before a bayonet charge; and the enemy hesitated to dash in on the dense masses of Union soldiers. Then suddenly the rebel left gave way, scattering over the field, but the rest stood firm, and poured forth a heavy fire upon the Federals. More infantry came up, and General Burnside found himself outnumbered, outflanked, and compelled to yield up the position he fought so bravely to win. He no longer attacked; but, with unfaltering firmness, defended himself, and sent to General McClellan for help. McClellan already knew of the sore strait to which Burnside was reduced, for his glass had not been turned away from the hard-pressed left of the field; but to send assistance was out of his power. In the valley, Porter’s fifteen thousand troops were impatient to join the fight; but when the two Generals, McClellan and Porter, looked into each other’s faces, each read in the other’s eyes, “They are the only reserves of the army—they cannot be spared.” As an answer to General Burnside’s desire for reinforcements, the Commander-in-Chief was obliged to reply: “Tell General Burnside this is the battle of the war. He must hold his ground till dark at any cost. I will send him Miller’s battery. I can do nothing more. I have no infantry.” Then as the messenger was riding away he called him back. “Tell him if he _cannot_ hold his ground, then the bridge, to the last man!—always the bridge! If the bridge is lost, all is lost.” Till Burnside’s message reached McClellan, no one anticipated that the battle could be concluded on that day; and few expected how near was the peril of total defeat. But suddenly and unexpectedly, the rebels halted, instead of pushing forward, and following up the advantage gained in recapturing the hill. As the twilight deepened into darkness, the fierce, wrathful cannonading ceased, and the long, desperately-contested battle of Antietam was over. For fourteen hours nearly two hundred thousand men, and five hundred pieces of artillery had been engaged in this memorable battle. The Army of the Potomac, notwithstanding the moral depression consequent upon its late severe reverses, had achieved a great victory over an army elated by recent successes; and, on the night of September 17th, the soldiers of the Union slept in peace and triumph on a field won by dauntless bravery, and covered with the dead and wounded, friends and foes, patriots and rebels.