At seven o'clock in the morning Burnside was ordered to have his corps in readiness for carrying the bridge in his front, crossing the stream, and attacking the Confederate right, which order he promptly obeyed. An hour later the order for this movement was issued by McClellan, but it did not reach Burnside till nine o'clock. The task before him was more difficult than his commander realized or than would be supposed from most descriptions of the action. The bridge is of stone, having three arches, with low stone parapets, and not very wide. On the eastern side of the stream, where Burnside's corps was, the land is comparatively low. The road that crosses the bridge, when it reaches the western bank has to turn immediately at a right angle and run nearly parallel with the stream, because the land there is high and overhangs it. As a matter of course, the bridge was commanded by Confederate guns advantageously placed on the heights. The problem before Burnside was therefore exceedingly difficult, and the achievement expected of him certain in any case to be costly. The task of first crossing the bridge fell upon Crook's brigade, which moved forward, mistook its way, and struck the stream some distance above the bridge, where it immediately found itself under a heavy fire. Then the Second Maryland and Sixth New Hampshire regiments were ordered to charge at the double quick and carry the bridge. But the fire that swept it was more than they could stand, and they were obliged to retire unsuccessful. Then another attempt was made by a new storming party, consisting of the Fifty-first New York and Fifty-first Pennsylvania regiments, led by Col. Robert B. Potter and Col. John F. Hartranft. By this time two heavy guns had been got into position where they could play upon the Confederates who defended the bridge, and with this protection and assistance the two regiments just named succeeded in crossing it and driving away the immediate opposing force, and were immediately followed by Sturgis's division and Crook's brigade. The fighting at the bridge cost Burnside about five hundred men. The Fifty-first New York lost eighty-seven, and the Fifty-first Pennsylvania one hundred and twenty. At the same time other troops crossed by a ford below the bridge, which had to be searched for, but was at length found. These operations occupied four hours, being completed about one o'clock P.M. Could they have been accomplished in an hour or two, the destruction or capture of Lee's army must have resulted. But by the time that Burnside had crossed the stream, captured a battery, and occupied the heights overlooking Sharpsburg, the fighting on McClellan's right was over. This left Lee at liberty to strengthen his imperilled right by bringing troops across the short interior line from his left, which he promptly did. At the same time the last division of his forces (A. P. Hill's), two thousand strong,