Union fighters who had previously occupied Chattanooga, Tenn., would see Confederate opponents pushing back this month 150 years ago in the war in hopes of retaking lost ground. Confederate fighters under the command of Braxton Bragg clashed with Union forces in late September of 1863 in northwest Georgia, amid a Confederate aime to recapture nearby Chattanooga, Tenn. The fighting erupted in earnest at Chickamauga in extreme northwest Georgia on Sept. 19 of that year. Combat raged for hours with the Union line stubbornly holding. But a Union general's attempt to shore up a perceived gap in his lines created an opening for Confederate James Longstreet to break through during a two-day battle before Union forces regrouped and stopped Longstreet's strike force. In the end, Confederates won a costly but critical battlefield victory. By Sept. 20, 1863, the secessionists had gained enough ground to begin positioning themselves on mountain heights around Chattanooga, menacing Union forces holding the city. All told, some 16,000 Union and 18,000 Confederate casualties were reckoned as the toll at Chickamauga — some of the bloodiest fighting in the so-called Western theater. The Confederate achievement would allow Bragg's army to besiege Union troops occupying Chattanooga enough to throttle the federal supply line for weeks. Fresh Union forces would begin arriving in the coming weeks and the Union's William T. Sherman would arrive by November before fighting later in 1863 would drive Confederates from the region.