But in the course of the sixteenth century men began here and there, somewhat timidly and tentatively, to rebel against the tyranny of antiquity, or rather to prepare the way for the open rebellion which was to break out in the seventeenth. Breaches were made in the proud citadel of ancient learning. Copernicus undermined the authority of Ptolemy and his predecessors; the anatomical researches of Vesalius injured the prestige of Galen; and Aristotle was attacked on many sides by men like Telesio, Cardan, Ramus, and Bruno. [Footnote: It has been observed that the thinkers who were rebelling against the authority of Aristotle--the most dangerous of the ancient philosophers, because he was so closely associated with theological scholasticism and was supported by the Church--frequently attacked under the standard of some other ancient master; e.g. Telesio resorted to Parmenides, Justus Lipsius to the Stoics, and Bruno is under the influence of Plotinus and Plato (Bouillier, La Philosophie cartesienne, vol. i. p. 5). The idea of "development" in Bruno has been studied by Mariupolsky (Zur Geschichte des Entwicklungsbegriffs in Berner Studien, Bd. vi. 1897), who pointed out the influence of Stoicism on his thought.] In particular branches of science an innovation was beginning which heralded a radical revolution in the study of natural phenomena, though the general significance of the prospect which these researches opened was but vaguely understood at the time. The thinkers and men of science were living in an intellectual twilight. It was the twilight of dawn. At one extremity we have mysticism which culminated in the speculations of Bruno and Campanella; at the other we have the scepticism of Montaigne, Charron, and Sanchez. The bewildered condition of knowledge is indicated by the fact that while Bruno and Campanella accepted the Copernican astronomy, it was rejected by one who in many other respects may claim to be reckoned as a modern--I mean Francis Bacon.