The last of Grant's forces were across the James by midnight of June 16th, while Lee took a more westerly and shorter route to Petersburg. The fighting there was continued as the two armies came up, but each Union attack was successfully repulsed. At the close of day on the 18th both opponents were in full strength and the greatest struggle of modern times was begun. Impregnable bastioned works began to show themselves around Petersburg. More than thirty miles of frowning redoubts connected extensive breastworks and were strengthened by mortar batteries and field-works which lined the fields near the Appomattox River. It was a vast net of fortifications, but there was no formal siege of Lee's position, which was a new entrenched line selected by Beauregard some distance behind the rifle-pits where he had held out at such great odds against Hancock and Smith. Grant, as soon as the army was safely protected, started to extend his lines on the west and south, in order to envelop the Confederate right flank. He also bent his energies to destroying the railroads upon which Lee depended for supplies. Attempts to do this were made without delay. On June 22d two corps of the Union army set out for the Weldon Railroad, but they became separated and were put to flight by A. P. Hill. The Federal cavalry also joined in the work, but the vigilant Confederate horsemen under W. H. F. Lee prevented any serious damage to the iron way, and by July 2d the last of the raiders were back in the Federal lines, much the worse for the rough treatment they had received. Now ensued some weeks of quiet during which both armies were strengthening their fortifications. On June 25th Sheridan returned from his cavalry raid on the Virginia Central Railroad running north from Richmond. He had encountered Hampton and Fitzhugh Lee at Trevilian Station on June 11th, and turned back after doing great damage to the railway. Ammunition was running short and he did not dare risk another engagement. Sheridan was destined not to remain long with the army in front of Petersburg. Lee had detached a corps from his forces and, under Early, it had been doing great damage in Maryland and Pennsylvania. So Grant's cavalry leader was put at the head of an army and sent to the Shenandoah valley to drive Early's troops from the base of their operations.