Augustin Theiner (b. at Breslau, 11 April 1804, d. at Civitavecchia, 8 August 1874) was a German theologian and historian.
He was the son of a shoemaker. As a boy he was a pupil at the gymnasium of St. Mathias at Breslau, and studied theology in the same city. Together with his brother Anthony he wrote, Einfuhrung der erzwungenen Ehelosigkeit bei den Geistlichen (1828). At the advice of this brother he abandoned theology and turned his attention to law, which he studied at Breslau and Halle, and in 1829 he obtained a degree in law at the latter university. He then received a scholarship from the Prussian Government, which enabled him to make researches in Belgium, England, and France as to the sources of Canon law. He finally went to Rome, where he settled permanently.
Here, under the influence of Count Reisach, then rector of the Propaganda and later cardinal, the change in his opinions was completed. In 1835 he wrote the Geschichte der geistlichen Bildungsanstalten, and in 1836 the Disquisitiones criticae, on the sources of canon law. Soon after this he became a priest and entered the Oratory of St. Philip Neri.
In the succeeding years he wrote the following works:
He was commissioned by Pius IX, who had given him a position in the Vatican Library in 1850, to write the Geschichte des Pontifikats Klemens XIV (1853; Italian translation, 1855). In this work he showed himself an opponent of the Jesuits, with whom he had been on good terms until 1844, so that the work was forbidden in the States of the Church.
In 1855 Pius IX appointed Theiner prefect of the Vatican archives. He now published his collections of authorities drawn from these:
Both before and during the Vatican Council he was in close connexion with the opponents of papal infallibility. Because he communicated to them the order of business of the Council of Trent, that had been kept secret, he was deposed from his dignities and offices.
Whether he died at peace with the Church is doubtful. His correspondence with the Old Catholic Professor Johann Friedrich during the years 1870-73 shows that he had the same views as the latter; on the other hand Count Hermann Stainlein asserts that he knew Theiner during this period as a loyal Catholic priest.
There is no doubt as to his large scholarship and his services to history. After his death appeared the work, Acta genuina Concilii Tridentini (1874), very imperfectly edited.
This article incorporates text from a publication now in the public domain: Herbermann, Charles, ed (1913). "Augustin Theiner". Catholic Encyclopedia. Robert Appleton Company.