He also occupied Lookout Mountain, west of the town, which Rosecrans had abandoned, and with it his control of the river and the river road as far back as Bridgeport.

The National troops were now strongly intrenched in Chattanooga Valley, with the Tennessee River behind them and the enemy occupying commanding heights to the east and west, with a strong line across the valley from mountain to mountain, and with Chattanooga Creek, for a large part of the way, in front of their line.
On the 29th Halleck telegraphed me the above results, and directed all the forces that could be spared from my department to be sent to Rosecrans.

Long before this dispatch was received Sherman was on his way, and McPherson was moving east with most of the garrison of Vicksburg.
A retreat at that time would have been a terrible disaster.

It would not only have been the loss of a most important strategic position to us, but it would have been attended with the loss of all the artillery still left with the Army of the Cumberland and the annihilation of that army itself, either by capture or demoralization.
All supplies for Rosecrans had to be brought from Nashville.

The railroad between this base and the army was in possession of the government up to Bridgeport, the point at which the road crosses to the south side of the Tennessee River; but Bragg, holding Lookout and Raccoon mountains west of Chattanooga, commanded the railroad, the river and the shortest and best wagon-roads, both south and north of the Tennessee, between Chattanooga and Bridgeport.