Leo XIII brought the Catholic Church into the modern industrial age. He became pope at 67 and reigned for 25 years, one of the longest papacies. His 1891 encyclical Rerum Novarum defended workers' rights to fair wages and trade unions, while rejecting socialism. It founded modern Catholic social teaching. He opened the Vatican Secret Archives to scholars. He encouraged the study of Thomas Aquinas. He was the first pope to be filmed on camera.
Key Milestones
1878: Pope – elected
1879: Aeterni Patris – Aquinas
1881: Archives – opened
1891: Rerum Novarum – encyclical
Pope Leo XIII (Italian: Leone XIII; born Gioacchino Vincenzo Raffaele Luigi Pecci; 2 March 1810 – 20 July 1903) was head of the Catholic Church from 1878 until his death in 1903. He had the fourth-longest reign and third-longest verified reign of any pope, behind those of St.