Throughout the afternoon, Confederate engineers scrambled to create a new defensive line 500 yards further south at the base of the Mule Shoe, while fighting at the Bloody Angle continued day and night with neither side achieving an advantage. At 4 a.m. on May 13, the exhausted Confederate infantrymen were notified that the new line was ready, and they withdrew from the original earthworks unit by unit. The combat they had endured for almost 24 hours was characterized by an intensity of firepower never previously seen in Civil War battles, as the entire landscape was flattened, all the foliage destroyed. May 12 was the most intensive day of fighting during the battle, with Union casualties of about 9,000, Confederate 8,000; the Confederate loss includes about 3,000 prisoners captured in the Mule Shoe.