According to legend, soap was discovered in Rome by women who washed their clothes in the waters of the Tiber River, at the foot of Mount Sapo. The substance that came down mixed with the waters of the river made both their hands and the clothes they washed remain sparkling clean.
At the top of Mount Toad, animal sacrifices were made to the Gods, and the animal fat, mixed with the ashes from the cremations, was carried down the mountain by the rains and mixed with other materials from the clay soil. This composition of fatty acids (animal fat) and potassium hydroxide (ash and water) gives rise to soap.
The chemical process that gives rise to soap is called saponification, a word that is probably due to the mountain sapo, like the word sapone (soap in Italian).