Bitter fighting raged for every ruin, street, factory, house, basement, and staircase. Even the sewers were the sites of firefights. The Germans called this unseen urban warfare "Rattenkrieg" ("Rat War"), and bitterly joked about capturing the kitchen but still fighting for the living room and the bedroom. Buildings had to be cleared room by room through the bombed-out debris of residential areas, office blocks, basements and apartment high-rises. Some of the taller buildings, blasted into roofless shells by earlier German aerial bombardment, saw floor-by-floor, close-quarters combat, with the Germans and Soviets on alternate levels, firing at each other through holes in the floors. Fighting on and around Mamayev Kurgan, a prominent hill above the city, was particularly merciless; indeed, the position changed hands many times.