They may initially have been cooked by hot stones in receptacles of natural substances, and then in utensils which could go straight over the fire.Soup, in fact, derives from sop or sup, meaning the sliced of bread on which broth was poured.
Food historians tell us the history of soup is probably as old as the history of cooking.
The act of combining various ingredients in a large pot to create a nutritious, filling, easily digested, simple to make/serve food was inevitable.
This made it the perfect choice for both sedentary and travelling cultures, rich and poor, healthy people and invalids.
Soup (and stews, pottages, porridges, gruels, etc.) evolved according to local ingredients and tastes.
New England chowder, Spanish gazpacho, Russian borscht, Italian minestrone, French onion, Chinese won ton and Campbell's tomato..all variations on the same theme.
Soups were easily digested and were prescribed for invalids since ancient times.
The modern restaurant industry is said to be based on soup.
Restoratifs (wheron the word "restaurant" comes) were the first items served in public restaurants in 18th century Paris.
Broth [Pot-au-feu], bouillion, and consomme entered here.