Aretaus was a famous Greek physician; exact details about his life are very obscure, including the dates of his birth and death. He seems to have been active in the first century of the common era.
The following is an adaptation of The Extant Works of Aretaeus, The Cappadocian, trans. Francis Adams. Boston: Milford House Inc, 1856.
§ 2.7. There are many other medicines [text missing] of the Celts, which are men called “Gauls,” those alkaline substances made into balls, with which they cleanse their clothes, called “soap,” with which it is a very excellent thing to cleanse the body in the bath.