Plato wrote the Republic around 380 BCE to discuss the philosophy behind justice, education, the ideal city, and the ideal citizen. The main character is Socrates, and he provides guidance on two types of education: one for the warrior-guardian class and one for the philosopher-king class.
The ideal education would include four areas of emphasis: music, sport (gymnastics), math, and dialectics (reasoned discourse using the Socratic method).
Students who are able to balance these four areas will find balance in in their lives.
In Book II, Socrates and the brothers Glaucon and Adeimantus go back and forth in dialogue about justice. Socrates suggests they should frame the discussion of justice in terms of the city rather than the individual. He uses the Warrior-Guardian as an example of one who needs to learn music, sports, and philosophy because he needs to be strong, but wise. Specifically, Socrates says Warrior-Guardians should be "philosophic, spirited, swift, and strong."
In Book III, Socrates delves more deeply into the specifics of education. For example, he suggests that warrior-guardians should learn from stories with simple narratives that teach moderation. Socrates also raises the question of telling the truth versus lying (for example, kings can lie for the good of the city and the people).
Overall, guardians should be temperate, moderate, and courageous. They should avoid heavy drinking, dramatic poetry, and laughter. They should be wise and efficient and learn to take care of the state. They should not question their teachers and should leave the deep thinking to the philosopher-kings.