Grierson rode into Baton Rouge on the 2d of May at the head of his own 6th Illinois and Prince's 7th Illinois cavalry, together 950 horse. Leaving La Grange on the 17th of April, he had within sixteen days ridden nearly 600 miles around the rear of Vicksburg and Port Hudson and along the whole line of the Jackson and Great Northern railroad. Beside breaking up the railway and the telegraph, and destroying for the time being their value to the Confederate army, Grierson's ride had an indirect effect, perhaps even more important than the direct objects Grant had in view when he gave his orders. That the railway should be rendered useless for the movement of troops and supplies, and the telegraph for the transmission of orders and intelligence, was of course the essential purpose of the operation, yet no one could have foreseen the extent of the confusion that followed, aided by Grierson's rapid movements, amid the fluttering and distracted councils at Vicksburg. Thus it happened that, when he heard of Grant's landing below Grand Gulf, Pemberton actually thought himself menaced by the advance of Banks, and this misapprehension was the parent of the first of those mistakes of his adversary of which Grant made such good use. Lieutenant Sargent,(1) the aide-de-camp sent to communicate with Admiral Farragut, as stated in the last chapter, found at the mouth of the Red River Admiral Porter, with the gunboats _Benton, Lafayette, Pittsburg_, and _Price_, the ram _Switzerland_, and the tugboat _Ivy_, with which he had run the batteries of Vicksburg in preparation for Grant's movement. Porter brought, indeed, no despatches, but he brought the great news that Grant had secured his landing at Grand Gulf and had begun his victorious march on Vicksburg. When Sargent returned to headquarters at Opelousas, he brought with him a despatch from Porter, promising to meet the army at Alexandria. Banks had already broken up the depots at Barré's Landing and New Iberia. On the afternoon of the 4th of May, he set Dwight in motion from his advance post at Washington. Weitzel marched from Opelousas at five o'clock the same afternoon, and Emory's division under Paine followed on the morning of the 5th. Emory, who had been suffering for some weeks, had at last consented to obey his surgeon's orders and go to New Orleans for a brief rest. Grover followed from Barré's Landing early in the afternoon of the same day. Banks himself remained at Opelousas until early in the morning of the 6th, having waited to receive and answer the translation of the cipher telegram from Grant; then he rode forward rapidly and joined his troops near Washington. From this time the communications of the army were to be by the Atchafalaya and the Red River.