At the start of the Battle of Berlin, the last major assault on Germany, the Russians attacked over the river Oder against German troops dug in on the Seelow Heights, about east of Berlin. Entrenchment allowed the Germans, who were massively outnumbered, to survive a bombardment from the largest concentration of artillery in history; as the Red Army attempted to cross the marshy riverside terrain they lost tens of thousands of casualties to the entrenched Germans before breaking through.