He entered the
Society of Jesus in Rome on 12 November 1814, shortly after the re-establishment of the order, and was professor of
humanities successively in the colleges of Terni,
Reggio Emilia,
Modena and
St. Andrew of the Quirinal. After completing his course and making his religious profession (1833), he became professor of rhetoric in the Roman College and held this position until 1842. Meanwhile, he devoted his leisure to study, applying himself through choice to non-Christian antiquities. He soon gave special attention to Christian antiquities, hoping thus to find a means of restoring Christian art. In 1838, he was made prefect of the
Kircherian Museum, a position he retained until his death. Marchi attempted a reorganization of the collection and produced a monograph on the ancient coins preserved there, the
Aes grave del Museo Kircheriano. In 1840, he announced his intention of collecting into one large publication the monuments of Christian architecture, painting, and sculpture. His archæological pursuits recommended him to
Gregory XVI as qualified to succeed Settele in the position of
Conservatore dei sacri cimiteni di Roma (1842), charged with supervising the early Christian burial places in and around the city. He brought to the study of early Christian monuments a new scholarly rigour. Art historian
Raffaele Garrucci was also one of Marchi's associates. These ancient cemeteries had been abandoned but thereafter were more accessible and could be studied on the ground. In spring 1842, Marchi conducted a tour of the
Catacombs of Saint Agnes for
James Roosevelt Bayley,
John Bede Polding, and a number of people from the
English College, Rome. In 1844, Marchi published the first volume of his "Monumenti", devoted to the construction of the catacombs, especially that of Saint Agnes. He proved the Christian origin of these ancient burial-places and, through his studies, brought about (21 March 1845) the discovery of the crypts of Saints
Peter and Hyacinth in the catacomb of
St. Hermes. In July 1855, his labours were interrupted for the first time by a stroke of
apoplexy, to which he succumbed in 1860. The notes intended for the continuation of the "Monumenti" were lost, but some of them were found by Giuseppe Bonavenia and made known at the Second Congress of Christian Archæology at Rome (1900). These recovered documents were destined for the second volume of the "Monumenti", which was to treat of the non-cemeterial Christian architecture of Rome. ==Published works==