Owing to its centrality in terms of archives and practices, yet its marginality in relation to the locations of mother Churches (e.g., Rome, Constantinople, Cairo), Jerusalem is a unique laboratory to study the diversity of Christian communities in the medieval period, their construction and interactions with each other and the surrounding Islamicate society. Unpublished and reputedly inaccessible, the archives kept by the Christian institutions in Jerusalem (Franciscan Custody, Armenian and Greek Patriarchates, St Mark’s Syriac Monastery) are now making it possible to uncover and study these interactions, which were often assumed and rarely proven due to a lack of sources. This paper aims to demonstrate if and how, in Jerusalem, inter-Christian and Christian-Muslim relations were more conductive to fluidity and heterarchy than to boundary-setting with the following question in mind: what are the places, actors and media of the connections between Christian communities and with the Mamluk authorities.