By March 7, 1945, the 9th Armored Division of the First Army captured the Ludendorff Bridge at Remagen. The First Army was the first enemy of Germany to cross the Rhine since the Napoleonic Wars. By the time the bridge collapsed after 10 days, the First Army had built two heavy duty bridges across the Rhine and established a bridgehead 40 kilometers (25 mi) long, extending from Bonn in the north almost to Koblenz in the south, and 10 to 15 kilometers (6.2 to 9.3 mi) deep, occupied by five U.S. divisions. They advanced slowly, waiting for Montgomery and the 21st Army Group to launch Operation Plunder across the Rhine on 23 March.