  Telesio dedicated his whole life to establishing a new kind of natural philosophy, which can be described as an early defense of naturalism and empiricism bound together with a rigorous criticism of Aristotelian natural philosophy and Galenic physiology. Telesio blamed both Aristotle and Galen for relying on elaborate reasoning rather than sense perception and empirical research. His fervent attacks against the greatest authorities of the Western philosophical and medical traditions led Francis Bacon to speak of him as “the first of the moderns” (Opera omnia vol. III, 1963, p. 114). He was perhaps the most strident critic of metaphysics in late Renaissance times. It was obviously due to his excellent relationships with popes and clerics that he was not persecuted and was able during his own lifetime to publish his rather heterodox writings, which went on the index shortly after his death. His principal work is the aforementioned De rerum natura iuxta propria principia (“On the Nature of Things according to their Own Principles”), which in the last augmented edition of the author's hand appeared in Naples in 1586. The De rerum natura is a huge treatise in nine books which deals with cosmology, biology, sense perception, reason and ethics. Another treatise of major importance is Quod animal universum ab unica animae substantia gubernatur. Contra Galenum, in which Telesio critizised central conceptions of Galenic physiology and psychology. This work was never printed, but circulated in manuscript copies (De Franco, 1981, p. XXII). Smaller treatises deal with a variety of themes such as colours, dreams, geology and meteorology, some of which were published in Rome in 1565 (De iis quae in aere fiunt et de terremotibus; De colorum generatione; De mari). Telesio's philosophy was disseminated by friends and students such as Tommaso Campanella,  whose writings contain long paraphrases of Telesian ideas; by Sertorio Quattromani, Telesio's successor as head of the Accademia Cosentina, who published a synthesis of his predecessor's philosophy in 1589; and by Antonio Persio, who gave lessons on Telesio's thought in Venice and published a collection of smaller works, the Varii de naturalibus rebus libelli, in 1590. Giordano Bruno speaks of the “giudiciosissimo Telesio” in the third dialog of De la causa, whilst Francis Bacon based his own speculative philosophy of nature on a blend of Telesian and Paracelsian conceptions (Giachetti Assenza 1980; Rees 1977; 1984). Thomas Hobbes followed Telesio in the rejection of species (Schuhmann 1990; Leijenhorst 1998, p. 116ff.) The physiology of René Descartes in De homine shows close similarities to Telesio's physiological theories as they are presented in De natura rerum (Hatfield 1992). Telesio also had some influence on Gassendi and on libertine thinkers (Bianchi 1992).