In the last 3000 years, whenever philosophy has taken a skeptical turn, there has been a great flowering of innovations, inventions, and discoveries. Philosophy in Ancient Greece, from 6th to 1st century BCE, was dominated by the skeptics—Xenophanes and Democritus were major skeptic philosophers of their time, and after them came the Sophists. In the 4th century BCE, Pyrrho founded the skeptic school of Pyrrhonism which continues to be influential till this day. Ancient Greek skepticism became very influential in the Roman Empire. When the Roman Empire went into decline in the 4th century, skepticism ceased to be the dominant philosophy, but it got revived in the 15th century through the works of Michel de Montaigne, Pierre Gassendi, and René Descartes. David Hume took skepticism to a new high in the 18th century. The Logical Positivists and the Analytic School, both of which denied the existence of metaphysics, dominated the philosophy of the 20th century.