Plato's ideal society, as outlined in his Republic, is primarily composed of two classes. The guardians are responsible for protecting the state, and are divided into two sub-classes: the rulers and auxiliaries. Rulers are the wisest of the guardians, and establish laws for the rest of society to follow. The auxiliaries are soldiers who defend the state, but also preserve order inside the state and serve as an example for the rest of the citizenry to follow. The second class is the citizenry, or those who perform basic societal roles.
For Plato, the education of the guardians is central in his discussion of the ideal state. His theory of education rests on the notion of "mimesis," or imitation. In order to characterize the four classical virtues of courage, wisdom, justice, and temperance, the guardians are to imitate heroes found in poetry and those of a superior rank. However, the guardians may only read poetry that depicts heroes acting virtuously; otherwise, the guardians may learn that sometimes heroes act unvirtuously and thereby act unvirtuously themselves.
The guardians are also instructed to simultaneously study music and gymnastics. Music, according to Plato, awakens the individual's passion, thereby motivating them to serve the state. Music also soothes the individual, which balances out what Plato claims are the negative consequences of gymnastics, or exercise. Exercise, for Plato, makes one hostile and aggressive. The proper balancing of music and exercise then allows the guardian to be courageous and capable in war, but also calm, collected, and willing to serve the polity.
Through this education, Plato concluded that the guardians, and by extension the citizenry since the guardians serve as role models for the citizenry, could best rule themselves and thereby establish a strong, stable society.