The Renaissance was a period of expanding horizons, and one in which there was a vast increase in knowledge of the world and its inhabitants. At the same time Europeans were recovering Latin culture and a much more complete grasp of Greek literature. Science was developing. New horizons made previous truths seem wrong or parochial.
These discoveries provided Montaigne and other skeptics with a treasure chest of new facts which they used to increase our sense of relativity of all man's beliefs about himself and the world in which he lives.