A map drawn by Union soldier Robert Knox Sneden shows the location of Union and Confederate troops between Missionary Ridge and West Chickamauga Creek in the mid-afternoon on September 20, 1863, during the Battle of Chickamauga. After Confederate forces succeeded in breaking through the Union lines, the bulk of the Union forces retreated toward Chattanooga. Union general George H. Thomas and his men held onto a tenuous position on Snodgrass Hill and repulsed assault after assault. For his actions that day Thomas earned the nickname "the Rock of Chickamuga"; shortly thereafter he was promoted to command of the Army of the Cumberland.
Based largely on his wartime sketches and diaries, Union private Robert Knox Sneden left behind a five-volume memoir about the Civil War that he began late in the 1870s and finished many years later, as well as large scrapbooks containing his art. His collection, which is owned by the Virginia Historical Society in Richmond, includes some 5,000 handwritten pages and some 900 watercolors and maps, including this one. He was an eyewitness to many of the places and events he captured; however, he was not present at the Battle of Chickamauga, and based this rendering on other accounts.