The book traces the history of the monastery of Santa Maria in Campo Marzio, with particular attention to the part of the ancient complex that today is the seat of the Procurator to the Holy See of the Patriarchate of Antioch of the Syrians. The occasion for this editorial initiative is the centenary of the establishment of the Procurator in 1920. At that time, the monastery had long since been dismantled and taken away from religious life, interrupting a continuity whose origins date back to the 8th century, with an initial community of oriental nuns who then passed to the Benedictine rule, protagonists of a gradual expansion that over the centuries had affected the entire insula. The division of the monastic spaces took place after 1870, following the suppression of the religious corporations and the confiscation of their patrimony: the oldest part, with the sixteenth-century cloister and the oratory of St Gregory Nazianzen at its centre, was destined for other uses, while the nuns continued to live for some years in the buildings gravitating around the extra-cloistered church of Santa Maria della Concezione, until 1914, before they were granted to the Syriac Catholic Patriarchate of Antioch. The publication weaves the history of the complex in connection with that of the monastic community that inhabited it for about a thousand years. The volume concludes with a brief historical profile of the Procura, from its establishment to the present day, and a note on the recently completed architectural restoration work, which involved both the church and the part of the complex used as the Procurator's residential and representative offices.