To start talking about the history of soap making we have to understand the reality of soap. Soap is simply a salt that foams. A salt is what you get when you mix an acid and a base together. This process is called saponification. The acids and bases neutralize each other and a salt forms in the process. Soap is made from acidic oils and an alkaline solution. Oil and alkali must be in balance to make the perfect bar of soap.
Any unsaponified oils are called “super fats”, and they add a moisturizing effect to soaps making them more gentle on the skin. If the super fat is too much the soap will not lather, it will create a soft bar of soap, and it will have a shortened shelf life. Excess alkali, or “Free Alkali” is harsh and drying to sensitive skin.
Now speaking of history, it's really hard to tell exactly when soap or soap alike materials were invented or discovered. However, the earliest recorded evidence of the production of soap-like materials dates back to around 2800 BC in ancient Babylon. A formula for soap consisting of water, alkali, and cassia oil was written on a Babylonian clay tablet around 2200 BC. The Ebers papyrus (Egypt, 1550 BC) indicates the ancient Egyptians bathed regularly and combined animal and vegetable oils with alkaline salts to create a soap-like substance.
The Ebers Papyrus, is an Egyptian medical papyrus of herbal knowledge dating to circa 1550 BC.
In ancient Palestine ashes from the barilla plant along with olive oil were used to make soap. The process started by heating the oil for days and keeping it lukewarm while adding alkali ashes. Constant stirring was required until a trace starts to form. The mixture is then poured into molds and left to harden for 2 weeks before it's cut into bars. Aromatic herbs were often added to the soap such as yarrow leaves, lavender, germander, etc. This ancient method is still in use in the production of Nabulsi soap.