Babylon
Evidence of soap usage in Bablyon around 2800 B.C. has been unearthed in archeological excavations. For this time period, lye would have consisted of a mixture of wood ash and water. It is theorized that tribal people could have discovered this solution by washing cooking supplies which were laden with animal fat and cooking ash in water, inadvertently making the first soaps.
Romans
An old Roman legend of Mount Sapo suggests that lye was discovered by the ancient civilization, also by accident (as it had been in Babylon) during the first few hundred years B.C. Animal sacrifice was practiced atop Mount Sapo. When rain washed over the mountain, volcanic ash and animal fat flowed into the Tiber River below. The caustic lye solution that developed and became soap upon mixture with the fats of sacrificed animals made this area an ideal place of cleansing. This legend gave a name to the process of soap making--Saponification.
Nicolas LeBlanc
Around 1780, french chemist Nicolas LeBlanc synthesized a solution of sodium hydroxide that would comprise man-made lye. This is the ingredient in soap as it is known today.