I think you're referring to the Skeptics, which is a broad term that applied to a large range of Greek philosophers that argued that if you cannot confidently claim knowledge (i.e. back up your claim with hard data and proof), then you shouldn't make truth claims.
Example: There is an Earthquake in Athens. The priests of Poseidon use this as an excuse to increase offerings to the temple. Approaching a Skeptic, the priest asks for an offering in light of the recent tremblings. The Skeptic ask how the priest knows that Poseidon, whom the priest has never seen, and whom the priest did not witness causing the problem, knows that Poseidon caused the quake. The priest would cite a religious belief, of course, which the Skeptic would decry as impossible to verify and thus invalid.
Schools of Skepticism included the Stoics and the Cynics.
You're probably thinking of the 4 thinkers; Heraclitus, Socrates, Plato, & Aristotle.
The Renaissance is when the Enlightenment thinkers and Scientific Revolutionary thinkers questioned the Ancient Greek philosiphers like Aristotle.
plato
Sophists
i'm pretty sure it was euripides
Greek and Roman thinkers
Philosophers.
Great thinkers
socrates
Socrates and Aristotle
Socrates and Aristotle
Traditional greek dances