A letter is, necessarily, a mark of a relationship between sender and recipient. Bodies of letters, where they survive, can tell us about communities. One such example is John Hooper the martyrs’ letters dating from the reign of Mary I of England at the British Library and Emmanuel College Library, Cambridge, England. The martyrologist John Foxe and his colleague Henry Bull published many of these letters during the 1560s in the famous ‘Book of Martyrs’ and the lesser known ‘Letters of the Martyrs’. However, these printed versions often edit out personal greetings and commendations, which point to a much larger network, as well as sometimes obscuring the true identities of the recipients. The original manuscripts therefore point to a much larger active community of Protestants who were practicing their faith in England during the reign of Mary I than Foxe and Bull’s publications show. I reconstruct this network in collaboration with Dr Sebastian Ahnert (Department of Physics, University of Cambridge) from evidence in the letters and show that through statistical measures and visualization, network analysis allows us to identify key Protestants who do not feature prominently in Foxe and Bull’s publications. Many of these individuals are important sustainers of the community infrastructure, providing monetary, moral, and logistical support to the martyrs during their persecution (Figure). It also allows us to understand just how important individual martyrs were in maintaining a community beyond the prison and beyond their own lifetimes. This paper will also seek to answer why Foxe and Bull’s depiction of the underground Protestant community in England failed to conform to this reality.