Adam Badeau, Military history of Ulysses S. Grant from April 1861 to April 1865. Volume 1

But the position alone. When Rosecrans discovered the extent of his misfortune, he determined, if possible, to hold Chattanooga, but thought himself unable to do more. The whole army was at once withdrawn into the town, and, in two days, a formidable line of works was thrown up, so close that some of the houses were left outside. Missionary ridge, immediately south and east of Chattanooga, is about four hundred feet high, and three miles from the Tennessee. This was instantly occupied by Bragg, who followed Thomas rapidly on the 21st. Lookout mountain, on the west, is twenty-two hundred feet high, and about three miles off. It is a rugged, narrow ridge, a hundred and fifty miles long, but not more than a mile or two across. Its northern and eastern front looks down on Chattanooga, while on its western side lies a narrow valley, hardly two miles wide, the bed of Lookout river. Still west of this valley, Raccoon mountain rises, another lofty and wooded ridge, reaching far off into Alabama. The Nashville and Chattanooga railroad, by which all supplies were brought to the national army, runs along the southern bank of the Tennessee, and immediately under the Lookout mountain, then crosses the entrance to Lookout valley, and turns south and west towards Stevenson.

This valley and mountain, in an evil hour, Rosecrans determined to abandon. He supposed that it would be impossible to maintain communication with the troops that were stationed there, and of course impossible for troops to exist without communication