6th-century BCE pre-Socratic Greek philosophers Thales of Miletus and Xenophanes of Colophon were the first in the region to attempt to explain the world in terms of human reason rather than myth and tradition, thus can be said to be the first Greek humanists. Thales questioned the notion of anthropomorphic gods and Xenophanes refused to recognise the gods of his time and reserved the divine for the principle of unity in the universe. These Ionian Greeks were the first thinkers to assert that nature is available to be studied separately from the supernatural realm. Anaxagoras brought philosophy and the spirit of rational inquiry from Ionia to Athens. Pericles, the leader of Athens during the period of its greatest glory was an admirer of Anaxagoras. Other influential pre-Socratics or rational philosophers include Protagoras (like Anaxagoras a friend of Pericles), known for his famous dictum "man is the measure of all things" and Democritus, who proposed that matter was composed of atoms. Little of the written work of these early philosophers survives and they are known mainly from fragments and quotations in other writers, principally Plato and Aristotle. The historian Thucydides, noted for his scientific and rational approach to history, is also much admired by later humanists. In the 3rd century BCE, Epicurus became known for his concise phrasing of the problem of evil, lack of belief in the afterlife, and human-centred approaches to achieving eudaimonia. He was also the first Greek philosopher to admit women to his school as a rule.