The people of Vicksburg were requested to leave the town by the commander of the post: they declined to abandon their homes; but the heavy rain of shot and shell from the national gunboats compelled them to burrow in the sides of the hills for security, and families lived for weeks in these caves. Pemberton hoped to receive assistance from Johnston, who was organizing another army at Canton. The knowledge of this fact prompted Grant to order another assault on the 21st of May. His men were full of fight, and in this respect he was generally ready to gratify them. The most elaborate preparations were made for the great event, and as the prelude to the assault, the guns of the batteries and of the fleet in the river rained a deluge of shot and shell upon the city and its works. The thundering of guns shook the solid earth, and the place was girt with fire. At ten o'clock, after the bombardment had continued for several hours, the assault was made. The entire army pushed forward, and, though prodigies of valor were performed, the result was a failure. The strength of the works was too great to be carried by storm; but the spirit of the soldiers was unabated. Grant was obliged not only to press forward the siege vigorously, but to keep a lookout upon Johnston in his rear. He was reënforced, so that by the middle of June he had seventy-five thousand troops, one half of whom formed the line in the trenches, while the other half constituted an army of observation, to watch the movements of the enemy in the rear. Grant was untiring in his labors, and felt that he had the place already. He had decided to save his men by regular siege operations. But the glorious day was at hand. On the morning of the 3d of July, a white flag was displayed on the rebel works, and two officers came out, announcing that they were the bearers of a sealed communication from General Pemberton to General Grant. They were conducted to the most convenient headquarters, and the commander of the Union army notified of the fact. Pemberton proposed an armistice for the purpose of making terms for the surrender of Vicksburg. He stated that he submitted the proposition in order to save the effusion of blood, which must otherwise be shed to a frightful extent, for he felt fully able to maintain his position for an indefinite period. General Grant replied, by letter, that the effusion of blood could be ended at any time by the unconditional surrender of the city and garrison. He complimented the endurance and courage of the defenders of Vicksburg, and assured the rebel general that they should be treated with respect as prisoners of war; but he had no other terms than unconditional surrender. General Bowen, the bearer of the letter, desired to see General Grant, who promptly declined to meet him, but consented to see Pemberton himself at three o'clock in the afternoon. The messengers returned to the city, and hostilities were immediately resumed, and continued till noon.