The story told in 1,000 B.C. Rome, about the discovery of soap on Sapo Hill, has been repeated so often that mythical elements have taken on factual proportions.
This is how the story goes: Women did their laundry at the base of Sapo Hill and at a higher elevation animal sacrifices had taken place. The women noticed that their laundry was coming out cleaner when they washed it in the soapy clay substance that oozed down the hill into the water. It was later discovered that this cleansing substance was formed when the rendered animal fat soaked down through the wood ashes and into the clay soil.
This version of the story is told in The Natural Soap Book by, Susan Miller Cavitch
So, from this discovery, soap was made much the same way by our grandparents. Water was usually collected in a rain barrell filled with wood ashes making lye, or Sodium Hydroxide. Some of these earlier soaps were harsh or lye heavy, because they did not have accurate ways to weigh or measure the lye. Today Sodium Hydroxide is much more consistent, and is easier to make a mild and gentle soap where all of the sodium hydroxide has saponified fully with the oils.The end result is a bar of soap with no sodium hydroxide present. Soap makers today do a process called superfatting, where they add more oils than are needed to react with the sodium hydroxide. This method leaves extra oils in the soap, therefore becoming more moisturizing to the skin.
I hope you enjoyed this step back in history to learn a little about how soap was discovered.