On the Songpan Grassland, the Red Army faced a severe test from extreme temperature variations between day and night and treacherous bogs that could swallow the unwary without warning. The greatest threat, however, was hunger. Crossing the grassland took many days. With no opportunity to replenish their meagre provisions, they soon ran out of food entirely.(Image source: The Red Ribbon on the Earth by Shen Yaoyi)