With his army in this mood and with a secure base behind him at Chattanooga, Bragg promptly moved upon Murfreesboro, with manifest intent to join Breckinridge and carry Nashville with a rush, if Rosecrans should fail to succor that strategic key to the situation. Murfreesboro lies on the Nashville and Chattanooga railroad, a scant forty miles southeast of Nashville. The country between is open and so completely unobstructed by physical features of difficulty, that the railroad shows scarcely a curve in its course between the two points. In view of Bragg's advance there was but one course open to Rosecrans. He must strengthen the defenses of Nashville and concentrate there for defensive and offensive operations. He promptly threw a strong force into Nashville and soon his entire army was concentrated there, except such detachments--and these were large--as were employed in rebuilding the railroad between Louisville and Nashville, which the Confederates had destroyed, and those other and still larger detachments which were necessary to defend that vitally important line of communication against the ceaseless activity of Forrest and Morgan, who were making themselves destructively ubiquitous. Rosecrans's activity was such that he succeeded in rendering Nashville secure before Bragg could carry out his purpose of assailing that stronghold. Still Bragg did not despair of his purpose. He sent peremptory orders to the forces around Corinth, either to send him strong reinforcements or to carry on such a campaign in their own districts as should compel Rosecrans to weaken himself at Nashville by sending heavy reinforcements to the west. Meanwhile Bragg fortified himself at Murfreesboro, establishing his lines along and across Stone river--a little, easily fordable stream--about two miles in front of the town. Rosecrans decided to assail him there, and to that end advanced with 47,000 men. His march began on the twenty-sixth of December, and by the thirtieth he was in position to assail his enemy with an effective force of 43,700 men. His plan of battle was to throw forward his left wing in force, envelope his enemy's right and crumple up his lines by pushing into action a ceaseless stream of fresh troops, wheeling his divisions to the right as they should be successively brought into action.