Lumen in caelo (light in the sky) is the motto which summarizes St. Malachy’s prophetic vision regarding the pontificate of Vincenzo Gioacchino Pecci (Leo XIII), the bicentenary of whose birth is marked this year. His papal coat of arms depicts a comet in the sky above a cypress tree. Gifted with great knowledge and a passionate interest in the Latin language in which he excelled from an early age, he studied under the Jesuits in Viterbo at the Collegio Romano. He was ordained a priest at the age of 27 and was sent first to the diocese of Benevento and later to that of Perugia, where he remained for almost 30 years. He was also a nuncio to Belgium and to Germany. He was elected the 256th pope and is remembered for the 86 encyclicals he wrote, also as a way to overcome the isolation in which the Holy See found itself after the unification of Italy. His most famous encyclical was Rerum Novarum (1891), which marked a turning point in the history of the Catholic Church. It was the first time the Church addressed the reality of Italian life at the time, marked by social conflict due to the particular historical and political circumstances. Reflecting on this reality, the encyclical called for a united response from the Church, the State and civil society to find ways to resolve the “social question”. For this reason Leo XIII became known as the “the workers’ pope” and “the social pope”. Contrary to the shorter predictions, his pontificate lasted 25 years and marks the third longest in history. Leo XIII died on 20 July 1903 and was entombed in the Basilica of St. John Lateran. The bicentenary of his birth represents a very relevant occasion today, also in relation to the recent encyclical Caritas in Veritate by His Holiness Benedict XVI, which makes explicit references to Rerum Novarum.