Passage: Stalin rushed all available troops to the east bank of the Volga, some from as far away as Siberia. All the regular ferries were quickly destroyed by the Luftwaffe, which then targeted troop barges being towed slowly across the river by tugs. It has been said that Stalin prevented civilians from leaving the city in the belief that their presence would encourage greater resistance from the city's defenders. Civilians, including women and children, were put to work building trenchworks and protective fortifications. A massive German air raid on 23 August caused a firestorm, killing hundreds and turning Stalingrad into a vast landscape of rubble and burnt ruins. Ninety percent of the living space in the Voroshilovskiy area was destroyed. Between 23 and 26 August, Soviet reports indicate 955 people were killed and another 1,181 wounded as a result of the bombing. Casualties of 40,000 were greatly exaggerated, and after 25 August the Soviets did not record any civilian and military casualties as a result of air raids.

Question: Why were civilians forced to stay?
presence would encourage greater resistance from the city's defenders