Giovannin Domenico Campanella, born at Stilo in Calabria in 1568, already at the tender age of fourteen had donned the cloth of the Dominican order, inspired by his readings of Albertus Magnus and Thomas Aquinas. Having soon tired of Aristotelianism and the Scholastic tradition, he devoted himself to Plato, Pliny, Galen, the Stoics and Democritus, but above all to Telesio (1509-1588), fascinated by his free philosophy, which rejected authority in his constant appeal to the senses and nature. Drawn by a desire to know Telesio personally, he went to Cosenza to meet him, but when he got there discovered that Telesio was deceased. Aside from Telesio's naturalism, Campanella's readings of the texts of the Platonic and ancient medical traditions occupied the years preceding his abandonment of religious orders and his consequent removal to Naples, where his contacts with Giovambattista Della Porta (1535-1615) and the influence of the Renaissance tradition of sorcery and astrology enabled him to reconcile the two components of his formation, Telesio's naturalism and Platonic spiritualism. In defense of Telesio he wrote his Philosophia sensibus demonstrata (Naples, 1591) and his Telesianism caused him to be tried and, should he ever set foot again in Calabria, imprisoned. But Campanella ignored all this and began to travel throughout Italy, in Rome, in Florence in search of a teaching post, and in Bologna. During his travels he was tried for sodomy and then for heresy, his manuscripts were repeatedly seized, and he was imprisoned, until finally he was obliged to return to Calabria, where under the cover of monastic seclusion he secretly planned a revolt. His intention of bringing about a comprehensive reform that would embrace philosophy, religion and politics failed miserably, and the anti-Spanish insurrection that broke out in 1599, inspired and led by Campanella as a kind of prophet at the head of a rabble of corrupt friars and outlaws on the run, was quickly suppressed. After a combined civil and religious trial for sedition and heresy, he was condemned. By faking insanity he avoided execution, which many of his companions were not spared, but spent the next twenty-seven years in a Naples prison, during which time he wrote all his works, City of the Sun, De sensu rerum, Metaphysics, Atheismus triumphans, Astrologica, Philosophia realis, Philosophia rationalis, amid confiscations, dispersions, rewritings and attempts at publication, only a few of which by sheer luck went through. When he left the Castel dell'Ovo in 1626 he was at once arrested by order of the Pope and shut in the prisons of the Sacred Office, from which he was soon released, but faced with the hostility of the Roman ecclesiastical environment he preferred to go to France, where he devoted himself at last to the publication of his complete works, abruptly interrupted by his death in 1639.

Despite his Apologia pro Galileo written in 1616 (but only published in 1622), his continual effusions of esteem and offers of help during Galileo's 1633 trial, Campanella never received much attention in return, and Galileo, probably baffled by the instinctive exuberance of his admirer, always preferred to keep his distance and never went beyond a cool and formal respect.