In Rome, at the time of Pliny (whose writings about health were scarcely received in the history of medicine), the close relationship between health and life style had already become a commonplace, as well as the idea of mesótes, that is to say health intended as the balance of opposites: several documents prove it, as for example the works of Celsus, Cicero and Plutarch. In De sanitate tuenda, Plutarch emphasizes the importance of a metría díaita, and presents a list of suggestions concerning the periods of rest, diet, training exercises, hygiene. In the letters, Pliny goes back to facts of the past and to personal experiences, explaining the concept of cura sui by means of a precise valetudinis ratio: he suggests moderatio and temperantia as the only ways to reach a perfect life style, that is to say the results of a specific behaviour that he considers as fundamental: temperare. From the examples given by Pliny in his letters we can understand the principles of dietetics inspired by temperamentum, that has to be the basis of every part of our life: day planning, choice of an appropriate home, balance between otium and negotium, diet.