Confederate line of battle in woods at Chickamauga.
From Battles and Leaders of the Civil War.

The Battle of Chickamauga (continued)

SEPTEMBER 19—FIRST DAY. Early in the morning of September 19, Thomas ordered Brannan forward to reconnoiter the Confederate forces which had crossed the Chickamauga. In this manner, Col. John T. Croxton's brigade of infantry accidentally ran into some of Forrest's cavalry, which were dismounted and serving as infantry, at Jay's Mill near Reed's Bridge. And so the battle began.

Maj. Gen. George H. Thomas, "The Rock of Chickamauga." Courtesy National Archives.

Croxton drove Forrest back, but reinforcements hurried to the latter forced Croxton to give ground. Suddenly the commanding generals realized that a major conflict was upon them, and they hurriedly sent troops into the fight as first one side and then the other gained the upper hand. Rosecrans, by rapid and forced marches, brought up his troops from Crawfish Springs. Bragg ordered his left wing divisions to cross to the west side of the Chickamauga. By mid-afternoon major fighting had spread along a jagged line some 3 miles in length. All the Union divisions, with the exception of Granger's reserve force, became involved. The Confederate troops were also largely engaged, except Hindman and Breckinridge who crossed over during the late afternoon and night.

When the battle ended for the day, little progress could be shown by either side. The fighting had been furious and without much plan. Bragg's troops had reached the LaFayette-Chattanooga Road but were not able to hold the position. Neither side could claim a victory. Bragg had failed to crush the Union left, and Rosecrans remained in possession of the roads to Chattanooga. The losses on both sides were heavy.

As night fell and darkness settled over the battlefield the fighting stopped, but there was little rest for the weary soldiers. Rosecrans brought the Army of the Cumberland into a more compact defensive line; Thomas' Corps, heavily reinforced, formed the left in a bulge east of the LaFayette Road at Kelly's Field.

Throughout the night the Confederates heard the ring of axes as the Union troops cut trees and logs to form breastworks. McCook's Corps in the center faced LaFayette Road; Crittenden's Corps on the right was a little withdrawn west of the road.

During the night, Longstreet arrived with two more brigades ready for action. Bragg then decided to form the Army of Tennessee into two wings for offensive action the next day. He placed General Polk in command of the right wing and General Longstreet the left. The Confederate Army, facing west between Chickamauga Creek and the LaFayette Road formed a line more or less parallel with the road.