Upon reaching Chancellorsville on April 30, 1863, General Joseph Hooker deployed the Army of the Potomac in a defensive perimeter around the intersection, with General Henry W. Slocum's Twelfth Corps holding the center of the Union line. For three days the troops entrenched, creating a sturdy earthwork screened by a line of fallen trees known as an abatis, and the trench there is a remnant of that fortified line. At first the Confederates did not test Slocum's position, but on May 3 Lee ordered a general assault. While Virginians led by General William Mahone attacked the works in front, Confederate artillery on the Orange Plank Road and at Hazel Grove sent shells into Slocum's line from the rear. The Twelfth Corps held its ground, but as the hours passed its ammunition ran low, and at 9 a.m. Slocum ordered a retreat. Colonel Charles Candy recalled that during the night instructions were received to fell the timber in front to form an abatis, which the men improved by building a breastwork and throwing up dirt with bayonets, swords, tin plates, and their hands, completing an intrenchment that resisted repeated attacks from the front.