Fritz Kretzschmer, La technique romaine (Brussels, 1966), cited in Hodge, Aqueducts, p. 454, n. 77. Citing Roto-Rooter’s History of Plumbing, Dan Berger, the administrator of the MadSci Network (a collection of scientists of various disciplines answering questions, at, says that toilet paper as we know it was not invented until about 1880. Before that, paper would have been too expensive for this purpose. Likewise cloth, although it could be washed and reused. Leaves were largely unavailable in urban areas. According to Berger, for most of human history “the preferred tool” was the left hand, presumably with water.