Sarpi's work attained such fame that the Vatican opened its archives to Cardinal Francesco Sforza Pallavicino, whom it commissioned to write a three volume rebuttal, entitled the "Istoria del Concilio di Trento, scritta dal P. Sforza Pallavicino, della Comp. di Giesù ove insieme rifiutasi con auterevoli testimonianze un Istoria falsa divolgata nello stesso argomento sotto nome di Petro Soave Polano" ("The History of the Council of Trent written by P. Sforza Pallavicino, of the Company of Jesus, in which a false history upon the same argument put forth under the name of Petro Soave Polano is refuted by means of authoritative testimony", 1656–1657). The great nineteenth century historian Leopold von Ranke ("History of the Popes"), examined both Sarpi and Pallavicino's treatments of manuscript materials and judged them both as falling short of his own strict standards of objectivity, but he rated the quality of Sarpi's work very highly, nevertheless, considering him superior to Guicciardini. Sarpi never acknowledged his authorship, and baffled all the efforts of Louis II de Bourbon, Prince de Condé to extract the secret from him.