The Germans had dug a complicated network of trenches around the building and a collapsed tunnel had filled with water from the Spree forming a moat across Königsplatz. The initial infantry assault was decimated by cross fire from the Reichstag and the Kroll Opera House on the western side of Königsplatz. By now the Spree had been bridged and the Soviets were able to bring up tanks and artillery to support fresh assaults by the infantry, some of which were tasked with out-flanking the Opera House and attacking it from the north-west.