The sixth encyclical, Aeterna Dei sapientia, commemorated the death of Pope Leo I and called for unity within Christendom from external movements such as Communism and secularism.
Ensiklik keenam, Aeterna Dei sapientia, mengenang kematian Paus Leo I dan menyerukan persatuan dunia Kristen dari gerakan-grakan luar seperti Komunisme dan Sekulerisme.