I found the large soup pot, made sure it was clean, and set it on the stove top.  I chose the ingredients I wanted to use in the soup and set them on the table.  Then I started the spice base for the soup by cutting up an onion in thin slices, and crushing a few cloves of garlic.  I put about a tablespoon of butter in the pan and turned on the heat to melt it, then added the onions and garlic to saute.  While they cooked, I cut up the vegetables.  I cut carrots into thick slices, and potatoes into one inch cubes, leaving the skin on for extra vitamins. Fresh green beans were trimmed and cut into one inch lengths. Then I put the vegetables in the soup pan and stirred them before adding six cups or so of water and heating it to a boil. Turning it down to simmer, I let it cook until the vegetables were soft enough to eat. 
Question: How did they heat the soup?
On the stove