<P> The first crossing of the Tennessee River was accomplished by the XX Corps at Caperton's Ferry, 4 miles from Stevenson on August 29, where construction began on a 1,250 - foot pontoon bridge . The second crossing, of the XIV Corps, was at Shellmound, Tennessee, on August 30 . They were quickly followed by most of the XXI Corps . The fourth crossing site was at the mouth of Battle Creek, Tennessee, where the rest of the XIV Corps crossed on August 31 . Without permanent bridges, the Army of the Cumberland could not be supplied reliably, so another bridge was constructed at Bridgeport by Maj. Gen. Philip Sheridan's division, spanning 2,700 feet in three days . Virtually all of the Union army, other than elements of the Reserve Corps kept behind to guard the railroad, had safely crossed the river by September 4 . They faced more mountainous terrain and road networks that were just as treacherous as the ones they had already traversed . </P> <P> The Confederate high command was concerned about this development and took steps to reinforce the Army of Tennessee . General Joseph E. Johnston's army dispatched on loan two weak divisions (about 9,000 men) from Mississippi under Maj. Gen. John C. Breckinridge and Maj. Gen. William H.T. Walker by September 4, and General Robert E. Lee dispatched a corps under Lt. Gen. James Longstreet from the Army of Northern Virginia . Only five brigades (about 5,000 effectives) from two of Longstreet's divisions arrived in time for the second day of the Battle of Chickamauga on September 20 . </P> <P> The three infantry corps of Rosecrans's army advanced by separate routes, on the only three roads that were suitable for such movements . On the right flank, McCook's XX Corps moved southwest to Valley Head, Alabama; in the center, Thomas's XIV Corps moved just across the border to Trenton, Georgia; and on the left, Crittenden's XXI Corps moved directly toward Chattanooga around Lookout Mountain . On September 8, after learning that Rosecrans had crossed into his rear, Bragg evacuated Chattanooga and moved his army south along the LaFayette Road toward LaFayette, Georgia . The Union army occupied Chattanooga on September 9 . Rosecrans telegraphed Halleck, "Chattanooga is ours without a struggle and East Tennessee is free ." Bragg was aware of Rosecrans's dispositions and planned to defeat him by attacking his isolated corps individually . The corps were spread out over 40 miles (65 km), too far apart to support each other . </P> <P> Rosecrans was convinced that Bragg was demoralized and fleeing to either Dalton, Rome, or Atlanta, Georgia . Instead, Bragg's Army of Tennessee was encamped at LaFayette, some 20 miles (32 km) south of Chattanooga . Confederate soldiers who posed as deserters deliberately added to this impression . Thomas firmly cautioned Rosecrans that a pursuit of Bragg was unwise because the Army of the Cumberland was too widely dispersed and its supply lines were tenuous . Rosecrans, exultant at his success in capturing Chattanooga, discounted Thomas's advice . He ordered McCook to swing across Lookout Mountain at Winston's Gap and use his cavalry to break Bragg's railroad supply line at Resaca, Georgia . Crittenden was to take Chattanooga and then turn south in pursuit of Bragg . Thomas was to continue his advance toward LaFayette . </P>

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