On the 23d of November, after a long and fatiguing march over roads almost impassable by reason of continuous rains, Sherman crossed the Tennessee by the pontoon bridge at Brown's Ferry, recrossed it above Chattanooga, and was assigned a position to the left of the main army near the mouth of Chickamauga Creek. Grant had now some eighty thousand men, of whom sixty thousand were on the scene of the coming battle, and, though fearful lest Burnside should be dislodged from his position at Knoxville, he would not be diverted from his purpose of sweeping the Confederates from the front of Chattanooga. It had been Grant's plan to attack on the 24th, but information reached him that Bragg was preparing a retreat. He, therefore, on the 23d, ordered Thomas to advance upon Bragg's center. Preparations for movement were made in full view of the Confederates; from the appearance of the troops, clad in their best uniforms, the advance line of the Southern army was content to watch this display, in the belief that the maneuvering army was parading in review. Suddenly, the peaceful pageant turned into a furious charge, before which the Confederate pickets, taken by surprise, retreated from the first line of earthworks, and Thomas, with little loss to either side, captured Orchard Knob, between Chattanooga and Missionary Ridge. From this point, which was almost a mile in advance of the position occupied during the morning, Grant directed the movements of his army on the following day. The Federal position was of less extent than that occupied by the Confederates. Sherman was in command of the left wing, while Thomas held the center, and "Fighting Joe" Hooker, with the Union right in Lookout Valley, threatened Lookout Mountain. The plan of battle was for Sherman to engage the Confederate right and sever communications between Bragg and Longstreet; Hooker was to carry out an assault on the Southern left flank, and at the same time maintain connection with Bridgeport. With both wings assailed by a superior force, it was believed that Bragg must reënforce these positions and permit Thomas, with overwhelming numbers, to concentrate upon the center. On the 24th, two distinct movements were in progress. Sherman met with but little opposition in his initial attack upon the Confederate right and promptly seized and occupied the north end of Missionary Ridge. The Confederates, late in the afternoon, fought desperately to regain the hill but were finally repulsed, and Sherman fortified the position he had gained. In the mean time, Hooker, early in the day, had begun his operations against Lookout Mountain. Standing like a lone sentinel above the surrounding valleys, its steep, rocky, and deeply furrowed slopes, rising into a high, palisaded crest, frowned defiance upon the advancing troops, while a well-constructed line of defenses completed the imposing barrier.