Protagorus used to lecture throughout Greece to students – today he would be probably be teaching in a university. He was one of the first of the group of philosophers known as sophists, which originally meant “expert” or “teacher” but came to describe philosophers who taught the skills of argument. Very little of his writing survives, but we know he wrote a book called On the Gods, in which he expresses an agnostic viewpoint:
“About the gods, I am unable to know whether they exist or do not exist, nor what they are like in form: for there are many things that hinder sure knowledge – the obscurity of the subject and the shortness of human life.”
He also said, “Man is the measure of all things”, a maxim which appeals to some humanists by putting humankind at the centre of the search for knowledge, but has also been criticised for its apparent relativism about truth.