The research started from the consideration that, although many aspects of the Milanese Early Renaissance are well known today, thanks to a vast literature, only few studies, so far, have paid attention to the ordinary world of architectural work - and its obscure protagonists - of this area and this period. Moving from the belief that this topic is crucial for a complete understanding of the 15th century architectural world, characterized by a progressive overlapping of roles and responsibilities in the worksites, this study aims to provide a contribution to expand the understanding of this matter, by focusing on a particular aspect of it: the role of the public administration in the architectural activity. In particular, the paper analyzes the characteristics of the "Office of the engineers of the Municipality of Milan", one of the major public architectural institution of the Duchy of Milan in the 15th century. Through an extensive archival survey, conducted in the major archives of Milan and Lombardy, the research achieves two main findings: a) the reconstruction of the complete Office staff throughout the 15th century and, b) an outline of the role and identity of the Office and its officers, through the elaboration of data collected. In particular, professional roles, technical duties, cultural background and tasks of the officers, together with Office management, appointment procedures and salary conditions are highlighted. This research, not meant as an ultimate study on the topic discussed, is intended to provide some material and reference points for further researches that will aim to expand the understanding of this matter.