Basin for bathing in a sitting position while partially immersing the body in water. Along the flat edge, there is a circular concavity used to hold pumice stone or soap. The anecdote, reported by Vitruvius (De architectura, IX, 9-13) in which Archimedes postulated the principle of physics that bears his name while he was immersed in a tub, confirms the frequent use of the baths, at least among some social classes, in Hellenistic society.