This unexpected turn of affairs utterly unnerved the Union General, and although he did manage by desperate exertions to collect his scattered army, he completely lost his head when Bragg attacked him at Chickamauga, Georgia, on the 19th of September, 1863, and before the savage battle of that name had ended he retired from the field, believing that his army had been totally destroyed. Such, undoubtedly, would have been its fate had not General Thomas and his brave troops covered the retreat, by holding the whole Confederate army in check for hours and even forcing it to yield portions of the bloody field. From that day forward Thomas was known as "The Rock of Chickamauga," but the heroic stand of his gallant men barely sufficed to save the Union army, which reached the intrenchments of Chattanooga only just in time, with the Confederates hot upon its trail. Had Bragg overtaken his flying opponent, he would doubtless have made an end of him then and there, but it was not altogether with regret that he saw him enter Chattanooga, for with the roads properly blocked he knew the place would prove a perfect trap. He, accordingly, began a close siege which instantly cut off all Rosecrans' communication with the outside world, except by one road which was in such a wretched condition as to be impossible for a retreating army. Indeed, the heavy autumn rains soon rendered it impracticable even for provision wagons, and as no supplies could reach the army by any other route, it was not long before starvation began to stare the besieged garrison in the face. Meanwhile, Rosecrans, almost wild with anxiety and mortification, sent dispatch after dispatch to Washington describing his condition and imploring aid, but though he still had an effective army under his command and plenty of ammunition, he made no attempt whatever to save himself from his impending doom. Day by day the situation grew more and more perilous; thousands upon thousands of horses and mules died for lack of food and the men were so nearly reduced to starvation that they greedily devoured the dry corn intended for the animals. All this time the authorities in Washington were straining every nerve to rescue the beleaguered army. Sixteen thousand men under General Hooker were rushed to its relief, provisions were forwarded within a day's march of the town, awaiting the opening of new roads, and finally, when the stream of frantic telegrams from the front showed that the army had practically no leadership, hurried orders were forwarded to Grant, authorizing him to remove Rosecrans, place Thomas temporarily in control and take the field himself at the earliest possible moment.