 During the twenty-seven years he spent imprisoned in Neapolitan castles (1599–1626), Campanella dedicated himself to the huge task of providing a new foundation for the entire encyclopedia of knowledge, writing, in addition to the works already mentioned, texts dealing with medicine, astrology, practical religion (in Quod reminiscentur he addressed eloquent appeals to members of all the religions of the world, aimed at persuading them to abandon irrational beliefs and to come together in Christian rationality), the Metaphysica, later printed in Paris, and a theological treatise in thirty books, whose publication, begun in the middle of the nineteenth century, is still in progress. One of the most interesting of his works is the Apologia per Galileo (Defense of Galileo). Written in 1616, when difficulties relating to natural theology first began to amass around Copernican and Galilean doctrines, and printed in Frankfurt in 1622, the Apologia represents an act of great courage and intellectual honesty on Campanella’s part, since he took up this delicate issue while he was still in prison and, furthermore, was not even defending his own doctrines. His own image of the book of nature, conceived as a living and organic entity, was far from Galileo’s picture of a book written in mathematical characters. Rather than a defense of heliocentrism, about which Campanella harbored grave reservations on account of its incompatibility with Telesian physics, the Apologia is a defense of the intellectual and academic freedom (libertas philosophandi) of Galileo and, more generally, of all Christian natural philosophers, whose first right and duty is to give preference to reading the book of nature over studying the books written by human beings. With great clarity, Campanella identifies the nub of the problem as the unjustified dogmatic value conferred on Aristotelian philosophy which, like all human doctrines, does not possess absolute and definitive certainty. All philosophies, in fact, must be modified, corrected or abandoned in light of our reading of the book of nature. In this brief work he draws on his immense theological knowledge to rethink in a profound and lucid manner the relationship between philosophy, science and theology. In a virtuoso demonstration of his hermeneutic abilities—on account of which the treatise in many places difficult going for the reader, who is in danger of getting lost in the thick tangle of citations—Campanella attempts to show how the longstanding union of theology and Aristotelian philosophy, regarded by theologians as necessary and unalterable, is in reality precarious, dated and in need of revision. Such a revision would pose no risk to theology; on the contrary, theology will be harmed by an obstinate and blind adherence to a system of physics that is no longer in agreement with new data and that rejects new discoveries. Abandoning Aristotelian philosophy not only would not bring about the collapse of theology, it would permit the recovery of a correct conception of science, one that must consist, as it did for Galileo, in a continual reading of the infinite book of nature, which is the expression of the infinite truth and of Christian rationality. On this basis Campanella invited Christianity to accept the rational and natural values of science with confidence and without unjustified fears, if it intended to set itself up as the authentic expression of Christ as the Word of God.