Marching from Cold Harbor, Meade's Army of the Potomac crossed the James River on transports and a 2,200-foot long pontoon bridge at Windmill Point. Butler's leading elements (XVIII Corps and Kautz's cavalry) crossed the Appomattox River at Broadway Landing and attacked the Petersburg defenses on June 15. The 5,400 defenders of Petersburg under command of Gen. P.G.T. Beauregard were driven from their first line of entrenchments back to Harrison Creek. After dark the XVIII Corps was relieved by the II Corps. On June 16, the II Corps captured another section of the Confederate line; on the 17th, the IX Corps gained more ground. Beauregard stripped the Howlett Line (Bermuda Hundred) to defend the city, and Lee rushed reinforcements to Petersburg from the Army of Northern Virginia. The II, XI, and V Corps from right to left attacked on June 18 but was repulsed with heavy casualties. By now the Confederate works were heavily manned and the greatest opportunity to capture Petersburg without a siege was lost. The siege of Petersburg began. Union Gen. James St. Clair Morton, chief engineer of the IX Corps, was killed on June 17.