Ah, soap. The true yardstick of civilization.

According to legend, Roman women washing clothing in the Tiber river noticed that the clothes came out cleaner in one certain area of the river: directly underneath the hill used for animal sacrifices (this was because the animal fat became lye as it washed down the hill into the river). It was around then (1000 BC) that the process of making soap from fat and lye was first understood and put into practice (in fact, the Sumerians in 3000 BC stumbled onto a method of creating a dilute soap solution with potash and fat, but they never separated the actual "soap" out of the mixture as the Romans did). The Roman ruins at Pompeii included a soap factory with completed bars of soap (probably for laundry, it was too harsh to be used on the skin).

Today, besides keeping us clean, soap provides us with a cheap and efficient source of napalm (Napalm is simply one part gasoline and one part soap) and nitroglycerine (as long as you have sulfuric acid and nitric acid as well)!