As Pemberton prepared to defend Vicksburg he was beset by difficulties rivaling those of his opponent, despite the topography which was friendly to his defensive purpose. Vicksburg would be secure only so long as the Confederate Army could prevent Grant from achieving a foothold on the high ground above or below the city. Yet, to prevent such a lodgment, it was necessary for Pemberton to defend a wide front extending 200 miles above and below Vicksburg, at any point along which Grant might strike. To cover this large area the Confederate commander would have to disperse his limited garrison dangerously and at the same time retain sufficient troops to protect the city—his primary responsibility. Under such conditions it was essential for Pemberton to receive information of Federal movements in order to concentrate his troops rapidly to meet the advance. Yet Pemberton was almost wholly lacking in cavalry and had no navy to interfere with and report Union progress through the rivers and bayous. Both Pemberton and Grant faced exacting problems in command during the Vicksburg operations. GRANT’S CANAL. Vicksburg’s location on the horseshoe bend of the river had suggested a solution to the Vicksburg problem the previous summer. By digging a canal across the peninsula below Vicksburg and diverting the river through it, unarmored transports could bypass the city batteries and deliver troops safely to the bluffs below. In January, Sherman’s Corps, assisted by dredging machines, began excavation of the mile-long canal. This project continued until March when a sudden rise in the river flooded the peninsula, driving the troops to the levees, and destroying much of their work. [Illustration: _Pivot-gun and crew of the Union warship _Wissahickon_, which fought the Vicksburg batteries._ From _Photographic History of the Civil War_.] [Illustration: GRANT’S CANAL _FEBRUARY-MARCH 1863_] By digging a canal across the mile-wide peninsula, Grant hoped to by-pass the Vicksburg batteries, move the army on transports below the city, and attack from the south. [Illustration: _Union soldiers at work on Grant’s canal opposite Vicksburg._ From a wartime sketch.] DUCKPORT CANAL. A similar effort to turn Vicksburg’s left flank was essayed by cutting a canal at Duckport, between Milliken’s Bend and Vicksburg. By this avenue it was hoped vessels might leave the Mississippi above Vicksburg, pass through a series of circuitous bayous and emerge again on the Mississippi 20 miles below the city. The route was laboriously opened for navigation and one small steamer safely passed to the river below. Then the level of the river fell and blocked the Duckport attempt. LAKE PROVIDENCE EXPEDITION.