To meet these powerful forces, whose destination he could not altogether foresee, Beauregard, who commanded in the west, concentrated his main army at Corinth, with smaller detachments scattered along the railroad to Chattanooga. The railroads on which he relied for supplies and reinforcements, as well as for communication with the eastern portion of rebeldom, formed an irregular parallelogram, of which the northern side extended from Memphis to Chattanooga, the eastern from Chattanooga to Atlanta, the southern from Atlanta to Jackson, Mississippi, and the western, by a network of roads, from Jackson to Memphis. The great East Tennessee and Virginia Railroad, which has not inaptly been called "the backbone of the rebellion," intersected this parallelogram at Chattanooga. Thus it will be seen that to destroy the northern and eastern sides of this parallelogram isolated Beauregard, and left East Tennessee, which was then almost stripped of troops, to fall easily before General Morgan. So important was this destruction of communication deemed by those in power, that it was at first intended to reach both sides, and destroy them by armies; but the distance was so great that the design of destroying it in this manner was abandoned. However, just at this time, J. J. Andrews, who was a secret agent of the United States, and had repeatedly visited every part of the South, proposed another method of accomplishing the same object, by means of a _secret_ military expedition, to burn the bridges on the road, and thus interrupt communication long enough for the accomplishment of the schemes which were expected to give rebellion in the southwest its death-blow. He first made the proposition to General Buell, who did not, for some reason, approve of it. Afterwards he repeated it to General Mitchel, who received it with more favor.