 Although little precise information is known, there can be not the least doubt that a great many individual cases concerning doctrinal orthodoxy are dealt with very thoroughly in the archives of the Congregation for the Doctrine of the Faith, simply because many theologians investigated by it have published some of the information within their own writings.Because hostility towards liberalism and socialism was so strong and the documents dealing with them considered very sensitive, at the time the papal files in the Vatican Secret Archives were opened by Leo XIII in 1879, that same Pope refused to allow any access to the archives either of the Inquisition or the Index of Forbidden Books.Even the pro-Papal historian Ludwig von Pastor could not use the Inquisition archive in writing his massive "History of the Popes since the End of the Middle Ages".