Gruel, and pottage generally, has been the primary source of food *especially* as peasant fare across the world. (Of pottage generally, it still is.)
Gruel was the staple food of the ancient greeks; bread was less common and eaten more sparingly, especially for travel.
In medieval Europe, the primary food made in villages would be a giant cauldron of gruel, shared by the entire community, continuously changing and rotating in ingredients.