Much more important than the whole of this circle was Balthasar Orobio de Castro (1620-1687). He also sprang from Marrano parents, who secretly continued to cling to Judaism, in that they abstained from food and drink on the Day of Atonement. In this meager conception of Judaism, Orobio was brought up. Endowed with clear intellect, he studied the decayed and antiquated philosophy still taught in Spanish academies, and became professor of metaphysics in the University of Salamanca. This fossilized philosophy appears neither to have satisfied him nor to have brought him sufficient means of subsistence, for he applied himself in riper years to the study of medicine. In this pursuit Orobio was more successful; he gained a reputation at Seville, was physician to the duke of Medina-Celi, and to a family in high favor with the court, and amassed considerable wealth. He was a happy husband and father, when the Inquisition cast its baleful glance upon him. A servant, whom he had punished for theft, had informed against him. Orobio was seized, accused of Judaism, and thrown into a narrow, gloomy dungeon, where he had not room to move, and where he spent three years (about 1655-1658).
At first he filled up his time with philosophical subtleties, as pursued at the Spanish universities. He undertook to defend a thesis, acting at the same time in imagination as the opponent, who interposes objections, and as the judge, who sums up and sifts the arguments. By degrees his mind grew so perplexed that he often asked himself, "Am I really Don Balthasar Orobio, who went about in the streets of Seville, and lived in comfort with his family?" His past seemed a dream, and he believed that he had been born in prison, and must die there. But the tribunal of the Inquisition brought a change into his empty dream-life. He was ushered into a dark vault, lighted only by a dull lamp. He could hardly distinguish the judge, the secretary, and the executioner, who were about to deal with his case. Having been again admonished to confess his heresy, and having again denied it, the hangman undressed him, bound him with cords, which were fastened to hooks in the wall, brought his body into a swinging movement between the ceiling and the floor, and drew the cords so tight, that the blood spurted from his nails. His feet, moreover, were strongly bound to a small ladder, the steps of which were studded with spikes. Whilst being tortured, he was frequently admonished to make confession, and was threatened, in case he persisted in denial, with the infliction of still more horrible pains, for which, though they caused his death, he would have to thank his own obstinacy, not the tribunal. However, he survived the torture, was taken back to prison to allow his wounds to heal, then condemned to wear the garb of shame (San Benito), and was finally banished from Spain. He betook himself to Toulouse, where he became professor of medicine in the university. Although respected in his new position, Orobio could not long endure the hypocrisy. He went to Amsterdam, publicly professed the Jewish religion, and assumed the name of Isaac (about 1666). No wonder that he became a bitter opponent of Christianity, which he had learnt to know thoroughly. He became an adherent of Judaism from conviction, proved himself a courageous and able champion of the religion of his fathers, and dealt such powerful blows to Christianity as few before him, so that a distinguished Protestant theologian (Van Limborch) felt compelled to reply to Orobio's attacks.