Meade’s Army of the Potomac marched from Cold Harbor to support Butler. Meade's leading XVIII Corps crossed the Appomattox River and attacked Petersburg on June 15. The Confederate defenders were driven back to Harrison Creek. The Union XVIII Corps was then relieved by the II Corps. The next day, June 16, II Corps captured another part of the Confederate line. Beauregard moved more defenders to hold the Union troops while Lee, now aware of the situation at Petersburg, rushed troops to the city. On June 18, the Union II, XI, and V Corps attacked but were beaten back with heavy casualties. Now the Confederate fortifications were heavily defended and all hopes of an easy Union victory were lost. This was the beginning of the siege of Petersburg. Rather than a tactical siege with short term goals, it now became a strategic siege involving a number of battles.