Monograph dedicated to an unknown project by Gio Ponti: the mother house of the religious congregation of Notre Dame de Sion, built in Rome between 1960 and 1965. The reasons and circumstances as to why the building has remained anonymous till now is unknown. The complete collection of project pencil drawings on tracing paper, preserved at the CSAC archives in Parma, have never been opened and are published here for the first time. In 2014, the building needed to be converted to house two important foreign Catholic universities (the Catholic University of America and the Australian Catholic University). There was a need for student residential and teaching buildings, which gave the architects Cinzia Abbate and Carlo Vigevano (AeV Architetti Associati) who edited this publication, the opportunity to carry out historiographic and philological research on the original project to establish the restoration project plans for the modern structure. The building was revealed thanks to the contribution of several experts of Ponti’s work: Maristella Casciato, Margherita Guccione, Salvatore Licitra, Elena Tinacci, Marina Kavalirek. The book is enriched with the addition of very detailed original drawings of the furnishings that still exist 50 years after the project was designed.