The Greeks developed many new ideas; some were highly influential and well-accepted and some were very controversial. Presocratic Philosophers were the first philosophers of the Western tradition. Later, the Academy in Greece was founded; Socrates became the first notable teacher in the Academy. He believed that improvement of the soul and questioning of everything was a necessity to learning. He was forced to drink poison hemlock because he questioned Athenian authority. His greatest student was Plato, who believed reason was the key to knowledge.
Plato came up with The Republic, a book that describes a government in which representatives of the people vote on decisions. He thought that philosophers would be the perfect fit for the representative role. His greatest student was Aristotle. Aristotle believed that experience was the right way to gain knowledge. Aristotle eventually founded and supplied the Lyceum.
After this philosophical golden age other systems appear, like The Cynicism, The Stoicism, The Epicureanism and The Skepticism.
The Greeks brought revolutionary material to the world. Some of their teachers were even killed for teaching it. Nevertheless, the ideas were extraordinary.