The Confederates now fell back to Big Black river.  Their line of communication with Jackson was cut.  A second battle was fought at Big Black River, and then, on the eighteenth of May, the victorious Union army surrounded Vicksburg, and the siege was begun.  The siege lasted forty-seven days, and was marked by heroic resistance on the one side and heroic pertinacity on the other, to the degree of making it one of the memorable events in the military annals of the world.  Gradually the Union lines were narrowed around the doomed town.  Ever nearer and nearer the lines of riflepits were drawn.  Day by day the resources of the Confederates were reduced.  But their defences were strong, and their courage for a long time unabated.

General Pemberton hoped and expected that an attack on Grant’s rear would be made in such force as to loosen his grip, and to enable the besieged to rise against the besiegers and break through.  The Confederates, however, had not sufficient forces for such an enterprise.  General Lee, in the East, had now undertaken the campaign of Gettysburg, and the Confederacy was already strained in every nerve.  General Grant had the way open for supplies and re-enforcements.  The siege was pressed with the utmost vigor, and Pemberton was left to his fate.

Meanwhile, however, two unsuccessful assaults were made on the Confederate works.  The first of these occurred on the day after the investment was completed.  It was unsuccessful.  The Union army was flung back from the impregnable defences in the rear of Vicksburg, and great losses were inflicted on them.  Grant, however, was undismayed, and, still believing that the enemy’s line might be broken by assault, renewed the attempt in a gallant attack on the twenty-second of May.  A furious cannonade was kept up for several hours, and then the divisions of Sherman, McPherson and McClernand were thrown forward upon the earthworks of the enemy.

It was here that General McClernand reported to the commander that he had gained the Confederate intrenchments.  General Grant says:  “I occupied a position from which I thought I could see as well as he what took place in his front; and I did not see the success he reported.  But his request for reinforcements being repeated, I could not ignore it, and sent him Quinby’s division.  Sherman and McPherson were both ordered to renew their assaults in favor of McClernand.  This last attack only served to increase our casualties, without giving any benefit whatever.”  In these attacks large numbers of the Federal soldiers had got into the low ground intervening, under the enemy’s fire, and had to remain in that position until darkness enabled them to retire.  The Union losses were very heavy, and General Grant, years afterward, in composing his Memoirs, referred to this assault and to that at Cold Harbor as the two conspicuous mistakes of his military career.