As Rosecrans moved toward the Tennessee River and Chattanooga, another Union army under command of General Burnside entered east Tennessee to threaten Knoxville. General Bragg, supposing that the two armies would join forces to attack him, made urgent appeals for help. Though the shortage of manpower at this time was a major problem of the Confederacy, troops were sent hurrying to Bragg from several directions. Rosecrans’ strategy, after viewing several possibilities, was to cross the river below Chattanooga, turn the Confederate left and interrupt his opponent’s communications and supply line from Atlanta. This movement if successful would effectively cut all railroad lines to Chattanooga, and Bragg would find himself shut in between Burnside on the north and east and Rosecrans on the west and south. To deceive Bragg as to the point of crossing the Tennessee River, Rosecrans sent Hazen’s and Wagner’s infantry brigades, Wilder’s mounted infantry, and Minty’s cavalry, all under the command of Brig. Gen. William B. Hazen, to make a feint at the river north of the town and to annoy the enemy as much as possible. [Illustration: _Union troops constructing a pontoon bridge across the Tennessee River at Bridgeport, Ala. Ruins of Nashville and Chattanooga Railroad bridge shown._ Courtesy Library of Congress.] The ruse was successful, and so thoroughly was Bragg deceived into thinking the attack would come from upstream on the north side of the Tennessee, he left the crossings below Chattanooga practically unguarded. Rosecrans with the bulk of his army then crossed the river in the vicinity of Bridgeport and Caperton’s Ferry, Ala., and Shellmound, Tenn. By September 4, the Army of the Cumberland, thus meeting little opposition, was safely across a great barrier and was threatening Bragg from new positions. When Bragg learned that the Union Army had crossed the Tennessee below Chattanooga and was threatening his supply lines, he decided after much deliberation to abandon his position and retreat southward. Once the Union Army had crossed the river, Thomas’ corps marched toward Trenton, Ga.; McCook’s took the road to Alpine, Ga.; and Crittenden moved toward Chattanooga. On the 9th of September, Rosecrans, believing the Confederates to be in full retreat, ordered McCook to press forward toward Alpine, covered by the cavalry, and make attempts to cut Bragg off; Crittenden to garrison Chattanooga with one brigade and pursue Bragg by way of the Ringgold Road with the rest of his force; and Thomas to continue toward Trenton.