4. Soon afterwards the Union forces were concentrated for the capture of Vicksburg. Three months were spent by General Grant in beating about the bayous around Vicksburg, in the hope of getting a position in the rear of the town. A canal was cut across a bend in the river with a view to opening a passage for the gunboats. But a flood washed the works away. Then another canal was begun, only to be abandoned. Finally, it was determined to run the fleet past the Vicksburg batteries. On the night of the 16th of April the boats dropped down the river. All of a sudden the guns of the enemy burst forth with shot and shell, pelting the passing steamers; but they went by with little damage. [Sidenote: Operations about Vicksburg.] 5. General Grant now marched his land-forces down the Mississippi and formed a junction with the squadron. On the 1st day of May he defeated the Confederates at Port Gibson. The evacuation of Grand Gulf followed immediately. The Union army now swept around to the rear of Vicksburg. On the 12th of May a Confederate force was defeated at Raymond. On the 14th of the month a decisive battle was fought near Jackson; the Confederates were beaten, and the city captured. General Pemberton, sallying forth with his forces from Vicksburg, was defeated by Grant on the 16th at Champion Hills, and again on the 17th at Black River Bridge. Pemberton then retired within the defences of Vicksburg. [Illustration: Vicksburg and Vicinity, 1863.] 6. The city was now besieged. On the 19th of May Grant made an assault, but was repulsed with terrible losses. Three days afterwards the attempt was renewed with a still greater destruction of life. But the siege was pressed with ever-increasing severity. Admiral Porter bombarded the town incessantly. Reinforcements swelled the Union ranks. Pemberton held out until the 4th of July, and was then driven to surrender. The defenders of Vicksburg, numbering thirty thousand, became prisoners of war. Thousands of small arms, hundreds of cannon, and vast quantities of ammunition and stores were the fruits of the great victory. 7. Meanwhile, General Banks had been conducting a campaign on the Lower Mississippi. From Baton Rouge he advanced into Louisiana, and gained a victory over the Confederates at Bayou Teche. He then moved northward and besieged Port Hudson, the last fort held by the Confederates on the Mississippi. The garrison made a brave defence; and it was not until the 8th of July that the commandant, with his force of six thousand men, was obliged to capitulate. [Sidenote: =Operations about Chattanooga.=] 8. In the latter part of June Rosecrans succeeded in crowding General Bragg out of Tennessee. The Union general followed and took post at Chattanooga, on the left bank of the Tennessee. During the summer Bragg was reinforced by the corps of Johnston and Longstreet.