Their plan at first was that Grant, with about 30,000 men, should move against the Confederate General Pemberton, who had about an equal force in the Tallahatchie river country, and occupy him there while Sherman, with 30,000 more, should descend the Mississippi in transports, convoyed by the gunboats, and effect a landing within striking distance of Vicksburg. Should Pemberton fall back for the defense of that stronghold, Grant was to press him with all possible vigor, endeavoring to cut him off from Vicksburg, and leave Sherman free to deal with that fortress as he pleased. The Tallahatchie country, through which Grant marched to assail Pemberton, is a tangled wilderness, lying actually lower than the surface of the Mississippi, and itself laced by multitudinous rivers, creeks, and streams, all of them difficult of passage, even at times of lowest water, and impossible of passage when a rain or a break in a Mississippi levée suddenly raises them to flood height. The region is, in fact, a vast morass. In parts of it the planters were often left for six, eight or ten months without communication with the outer world, except by way of the rivers themselves, during the winter. It is not difficult, even for the reader who has no technical knowledge of war, to understand how slowly and painfully a march through such a country must be made, when not only the cannon but a wagon train, carrying every ounce of supplies necessary for 30,000 men must be dragged at every step through a quagmire. But this was not Grant's chief difficulty. With his headquarters at Holly Springs, and a purpose to press forward in a southwesterly direction, he must maintain a long and attenuated line of communication with his base at Columbus, Kentucky. The Confederates were alert and ceaselessly active in assailing this line and rendering it hopelessly insecure. They sent heavy cavalry detachments under Van Dorn and Forrest to cut him off from his base, and Van Dorn, emboldened by repeated successes at last on the twentieth of December assailed Holly Springs itself, where Grant had accumulated many million dollars' worth of supplies in preparation for his campaign. The Confederate cavalrymen captured the town and its garrison, burned all the stores and destroyed the railroad buildings. In the meanwhile Forrest raiding farther north cut the railroad between Jackson, Tennessee, and Columbus, Kentucky, thus completely severing Grant's line, and leaving him in the enemy's country without supplies or the means of procuring them. In order to save his army Grant immediately abandoned his plan of campaign and moved northwestward to Memphis. His purpose now was to join Sherman there, unite the two wings of the army, and in company with Sherman and the gunboats move down the river and assail Vicksburg in overwhelming force.