In 1863 the Army of the Cumberland, under
Rosecrans, after crossing the
Cumberland Mountains in pursuit of the
Confederates under
Bragg, was stretched along the
Tennessee River from a point above
Chattanooga 100 miles westward.
Rosecrans determined to cross that stream at different points, and, closing around
Chattanooga, attempts to crush or starve the Confederate army there.
General Hazen was near
Harrison's, above
Chattanooga (Aug. 20). He had made slow marches, displaying camp-fires at different points, and causing the fifteen regiments of his command to appear like the advance of an immense army.
On the morning of Aug. 21 National artillery under
Wilder, planted on the mountain-side across the river, opposite
Chattanooga, sent screaming shells over that town and among
Bragg's troops.
The latter was startled by a sense of immediate danger; and when, soon afterwards,
Generals Thomas and
McCook crossed the
Tennessee with their corps and took possession of the passes of
Lookout Mountain on
Bragg's flank, and
Crittenden took post at Wauhatchie, in
Lookout Valley, nearer the river, the
Confederates abandoned
Chattanooga, passed through the gaps of
Missionary Ridge, and encamped on
Chickamauga Creek, near
Lafayette in
northern Georgia, there to meet expected National forces when pressing through the gaps of
Lookout Mountain and threatening their communications with
Dalton and
Resaca.
From the lofty summit of
Lookout Mountain Crittenden had seen the retreat of
Bragg.
He immediately led his forces into the
Chattanooga Valley and encamped at Ross's Gap, in
Missionary Ridge, within 3 miles See
Chickamauga, battle Mauga National Park. 
