Union inaction created the opportunity for the Confederates to attack first before Buell arrived. On the morning of April 6, 1862, Grant's troops were taken by surprise when the Confederates, led by Generals Albert Sidney Johnston and P.G.T. Beauregard, struck first "like an Alpine avalanche" near Shiloh church, attacking five divisions of Grant's army and forcing a confused retreat toward the Tennessee River. Johnston was killed and command fell upon Beauregard. One Union line held the Confederate attack off for several hours at a place later called the "Hornet's Nest", giving Grant time to assemble artillery and 20,000 troops near Pittsburg Landing. The Confederates finally broke through the Hornet's Nest to capture a Union division, but "Grant's Last Line" held the landing, while the exhausted Confederates, lacking reinforcements, halted their advance. The day's fighting had been costly, with thousands of casualties. That evening, heavy rain set in. Sherman found Grant standing alone under a tree in the rain. "Well, Grant, we've had the devil's own day of it, haven't we?" Sherman said. "Yes," replied Grant. "Lick 'em tomorrow, though."