CHAPTER XV. ON TO VICKSBURG. -- BOMBARDMENT OF THE CONFEDERATE STRONGHOLD. -- PORTER'S CRUISE IN THE FORESTS. While the smaller gunboats were thus making dashes into the enemy's country, destroying batteries and unfinished war-vessels, and burning salt-works, the heavier vessels of the fleet were being massed about Vicksburg, and were preparing to aid the army in reducing that city to subjection. We need not describe the way in which Gen. Grant had been rushing his troops toward that point, how for weeks his engineers had been planning trenches and approaches to the Confederate works, until toward the middle part of June, 1863, the people in that city found themselves hemmed in by a huge girdle of trenches, batteries, and military camps. Gen. Pemberton, with his army of Confederate soldiers, had been forced backward from point after point, until at last he found himself in Vicksburg, with the prospect of a long siege before him, and no way to get past the inexorable lines of blue that surrounded him. It is true that he had a wonderfully strong position, and many were the tongues that said Vicksburg could never be taken. But though stronger than Sebastopol, stronger than the Rock of Gibraltar, Vicksburg was destined to fall before that mighty army that encircled it, and was slowly starving the city into subjection. But the Union soldiers, looking from their camps toward the Confederate citadel, saw that they had before them some severe work before that flag that flaunted over the city should be replaced by the stars and stripes. The city stands on a towering bluff high above the eastern bank of the Mississippi River. On that frowning height the busy hands of Pemberton's soldiers had reared mighty batteries, that commanded the Mississippi for miles up and down stream. To think of carrying the works by assault, was madness. Sherman had tried, and was beaten back with terrible loss. Then Grant, with nearly twenty thousand men, and with the co-operation of the river-flotilla, came upon the stage, and determined to take the city though it kept him at bay for months.