Longstreet's principal lines were north of Knoxville beyond the railway and the station buildings. He also occupied a line of hills, but pushed forward strong skirmish lines and detachments to cover the making of intrenchments closer to the town. There were frequent bickering combats, but no general engagement. The enemy made efforts to destroy the pontoon bridge by sending down logs and rafts from above. These were met by an iron cable boom stretched across the river above the bridge, borne on wooden floats to keep it at the surface. [Footnote: Century War Book, vol. iii. p. 739.] Several efforts were made to drive Burnside's men from the hills covering the town on the south side of the river, but they were defeated, and communication was kept up with the valley of the French Broad River, and supplies enough were brought in to make it certain that Burnside could not be starved out, although the rations were reduced to the smallest quantity and the fewest elements which would support life. A week passed thus, Burnside being shut off from all communication with the outer world. The 25th of November came with the almost miraculous storming of Missionary Ridge by the army under Grant at Chattanooga. Bragg retreated southward and Longstreet had no longer a possibility of rejoining him. Yet Burnside knew nothing of it, and did not dream of the more than complete justification his slow defensive campaign was having, in the tout and demoralization of the Confederate army in Georgia in Longstreet's absence. The latter was now forced to attack the fortifications or to raise the siege of Knoxville. He knew, at least by rumor, what Burnside was ignorant of,--not only the defeat of Bragg, but that a force was already moving from Grant's army to the relief of Knoxville. Bragg had also sent to him a staff officer with exhortations to prompt action. For a day or two Longstreet tried to attract Burnside's attention to the south of the river and to other parts of the lines, and then on the 28th prepared a desperate assault upon the great salient of Fort Sanders.