Union fighters occupying Chattanooga, Tenn., would see Confederate opponents pushing back this month 150 years ago in the Civil War in hopes of retaking lost ground.

Confederate fighters under Braxton Bragg clashed with Union forces in late September of 1863 in northwest Georgia, amid a Confederate bid to recapture neighboring 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 allowed Confederate James Longstreet to break through during a two-day battle before Union forces pushed him back and held their ground. In the end, Confederates won a costly but critical battlefield victory.

By Sept. 20, 1863, the secessionists had gained enough ground to begin staking positions on mountain heights around Chattanooga, menacing

Union forces holding that 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 before later fighting in the year would drive Confederates away from Chattanooga for good.