The strategetic line of the Confederates was broken, and new dispositions of their forces became necessary on account of this important victory; Columbus was abandoned, and its men and material sent to Island No. 10. The battle of Pittsburg Landing, or Shiloh, as it is called in the South, followed under Grant's command. It was a bloody and hotly contested action, and not as decisive as that of Donelson. The ground was held, and the arrival of Buell with reinforcements caused the Confederates to retire. Sherman had a command in this battle under Grant, and the strong friendship between these two great commanders, which subsisted to the end, had its origin about this time. Not such were the relations between Halleck and Grant, for the latter was practically thrown into the shade by the former; but the hero of Fort Donelson continued to do his duty faithfully, making no issue with his superior. At this time he was in command of the Army of the Tennessee. While he remained in this position the Union army and navy had made decided progress in the West and the South; but no real advance was made in the direction of the rebel capital. Then McClellan was removed from his position of general-in-chief, and Halleck was appointed in his place. Grant seemed to be forgotten for the time, or his operations were overshadowed by those in the East. But he had driven the enemy out of West Tennessee, and was turning his attention toward Vicksburg. When he had sufficiently informed himself in regard to the situation, he proposed to the general-in-chief a movement upon Vicksburg, which was really the Gibraltar of the Mississippi, and he was invested with full powers to carry out his own plans. Constantly and earnestly supported by Sherman, he battered against this strong fortress for six months. Various expedients were resorted to for the reduction of the place, without success. With the written protest of four of his ablest generals in his pocket, Grant moved his army to a point four miles below Grand Gulf, fought several battles on his way, and came to the rear of Vicksburg. The Confederate engineers were doubtless as skilful as any in the world, and seemed to be justified in regarding the fortress, with its surrounding batteries, fortifications, swamps, and tangled jungles, as impregnable.