Vicksburg had long been the hard military problem of the Southwest. The city, which had been made a fortress, was at the summit of a range of high bluffs, two hundred and fifty feet above the east bank of the Mississippi River, near the mouth of the Yazoo. It was provided with batteries along the river front and on the bank of the Yazoo to Haines's Bluff. A continuous line of fortifications surrounded the city on the crest of the hill. This hill, the slopes of which were cut by deep ravines, was difficult of ascent in any part in the face of hostile defenders. The back country was swampy bottom land, covered with a rank growth of timber, intersected with lagoons and almost impassable except by a few rude roads. The opposite side of the river was an extensive wooded morass. In May, 1862, flag officer Farragut, coming up the Mississippi from New Orleans, had demanded the surrender of the city and been refused. In the latter part of June he returned with flag officer Porter's mortar flotilla and bombarded the city for four weeks without gaining his end. In November, 1862, General Grant started with an army from Grand Junction, intending to approach Vicksburg by the way of the Yazoo River and attack it in the rear. But General Van Dorn captured Holly Springs, his depot of supplies, and the project was abandoned. The narration, with any approach to completeness, of the story of the campaign against Vicksburg would require a volume. It was a protracted, baffling, desperate undertaking to obtain possession of the fortifications that commanded the Mississippi River at that point. Grant was not unaware of the magnitude of the work, nor was he eager to attempt it under the conditions existing. He believed that, in order to their greatest efficiency, all the armies operating between the Alleghanies and the Mississippi should be subject to one commander, and he made this suggestion to the War Department, at the same time testifying his disinterestedness by declining in advance to take the supreme command himself. His suggestion was not immediately adopted. On the 22d of December, 1862, General Grant, whose headquarters were then at Holly Springs, reorganized his army into four corps, the 13th, 15th, 16th, and 17th, commanded respectively by Major-Generals John A. McClernand, William T. Sherman, S. A. Hurlbut, and J. B. McPherson. Soon afterwards he established his headquarters at Memphis, and in January began the move on Vicksburg, which, after immense labors and various failures of plans, resulted in the surrender of that fortress on July 4, 1863.