Rosecrans did not advance again till June, although Bragg lay quite near. The latter fell back as the Unionists approached, first into Chattanooga and then over the Georgia line. Rosecrans followed. Bragg was now re-enforced, and determined to retake Chattanooga, which lay on the Tennessee River and was an important strategical point. The two armies met on Chickamauga Creek, twelve miles south of Chattanooga. All through the first day's battle, September 19th, there was hot fighting--charges and countercharges--but no decisive advantage fell to either side. During the night Bragg was reenforced by Longstreet's corps from Virginia, and he opened the next day's fight with an assault upon the Union left. Brigades were moved from the centre to support the left. Through the gap thus made Longstreet poured his men in heavy columns, cutting the Union army in two. Its right wing became demoralized, and fled toward Chattanooga in wild confusion, Rosecrans after it at a gallop, believing that all was lost. But all was not lost. General Thomas commanded the Union left. Like a flinty rock he stood while Polk's and Longstreet's troops surged in heavy masses against his front and flank. About three o'clock heavy columns were seen pouring through a gorge almost in Thomas's rear. They were Longstreet's men. It was a critical moment Granger's reserves came rushing upon the field. Raw recruits though they were, they dashed against Longstreet like veterans. In twenty minutes, at cost of frightful slaughter, the gorge and ridge were theirs. Longstreet made another assault, but was again repulsed. At nightfall Thomas fell back to Chattanooga, henceforth named, and justly, the "Rock of Chickamauga." For six hours he had held his own with 25,000 braves against twice that number. Out of 70,000 troops Bragg lost probably 20,000. Rosecrans's force was about 55,000, his loss 16,000. [Illustration: Portrait.] General George H. Thomas. Bragg proceeded to shut up the Union army in Chattanooga. Grant, now commanding the Department of the Mississippi, was ordered to recover Chattanooga, and his deeds along this front, though less often mentioned, will glitter upon the page of history with little if any less lustre than those about Vicksburg. Upon his arrival, late in October, he found the city practically in a state of siege. Its railroad communication with Nashville was cut off, and supplies had to be hauled in wagons sixty miles over a rough mountain road. The men had been for some time on half rations. Thousands of horses and mules had starved, and the artillery could not be moved for lack of teams. There was not ammunition enough for one day's fighting. In five days Grant wrested the railroad from Bragg's men and bridged the Tennessee, so that an abundant supply of food and ammunition came pouring in.