The centre of interest and anxiety now was Chattanooga, in East Tennessee, near the border of Georgia. The Confederates had been striving to retrieve the ground lost, since the fall of Fort Henry, by pushing northward in this direction. Halleck's dispersion of forces had sent Buell to this section, and Buell had been superseded by Rosecrans, a zealous and patriotic but unfortunate commander. The repulse at Chickamauga might have proved disastrous to his army but for the splendid behavior of the division under General Thomas, an officer not unlike Grant in the mould of his military talent, who there earned the sobriquet, "The Rock of Chickamauga." The army of Rosecrans had been gathered again at Chattanooga, where it was confronted by Bragg, whose force surrounded it in an irregular semicircle from the Tennessee River to the river again, occupying Missionary Ridge on one flank and Lookout Mountain on the other, with its centre where these two ridges come nearly together. Chattanooga was in the valley between, near the centre of which, behind the town, was an elevation, Orchard Knob, held by the enemy. Bragg commanded the river and the railroads. The route for supplies was circuitous, inadequate, and insecure, over mountain roads that had become horrible. Horses and mules had perished by thousands. The soldiers were on half rations. Word came to Grant in Louisville, that Rosecrans was contemplating a retreat. He at once issued an order assuming his new command, notified Rosecrans that he was relieved, and instructed Thomas to hold the place at all hazards until he reached the front.