Ante-Nicene Fathers Volume 5
Hippolytus: The Refutation of All Heresies
Plato's student Aristotle "reduced philosophy into an art, and was distinguished rather for his proficiency in logical science." Aristotle argued that there is one underlying stable principle ("substance"), but nine changing expressions of it ("accidents"). Aristotle mostly agrees with Plato, except concerning the soul (which is immortal for Plato, and permanent for Aristotle). Likewise Aristotle sees a good in the physical world, while Plato restricts it to matters concerning the soul. Aristotle's students get their name from their habit of teaching while wandering around the Lyceum, hence they are the 'Peripatetics.'
Zeno and the Stoics (named such because they met in the Stoa, the "porch") carried logic to its utmost, until they were strict fatalists with the Divinity as the source of all existence concerned with directing all creation. We then are like dogs tied to cars (presumably meaning "chariots"), we can trot along willingly or be dragged, but either way we are going. All we have control over is our response to what happens, not to what happens as such. For the Stoic, the soul is immortal but the world will end in a fiery cataclysm.
Epicurus stands against all others, holding to an atomic chaos in a vacuum. Even the deity is the product of chance, and however "eternal and incorruptible" it may be, God cares nothing for human history or existence--chance is all. So there is no afterlife, and so all our wisdom should be focused on pleasure. Of course, his students have differed on what "pleasure" is, some have thought physical pleasure, and others the pleasure of virtue...
The "Academics" (Skeptics) argue that we can't really know anything for certain, all we have are the appearances because everything is "in a state of flux and change." And so we should not make certain statements, only relative ones.
The Brahimins in India live ascetic vegetarian lives, living in naked (literally) simplicity, since the body is the clothing of the soul. The believe in a god to whom they pray wordlessly, but their god is corporeal, even if their own souls are spiritual and immortal. They do not fear death, and live in a way that reflects that.
The Druids follow Pythagoras to the extreme, and have worked a complex system that mixes math and magic.
Hesiod works the Olympian gods into a system that tries to be rational and explain nature, but which fails to "discern the God and maker of these."
All of these become sources of heresy, which Hippolytus will no proceed to go through. [Which he does in books II and III, which we do not have.]