Social network analysis of a disappeared Christianity: The Apostolic movement in Italy around 1300

Inquisition registers offer unique access to the relational fabric of medieval dissident groups. This chapter showcases common tools of social network analysis (SNA) for the historical study of religion, situating the approach within Historical Network Research, on the case of the Apostolic movement, a lay Christian group which emerged in thirteenth-century northern Italy and was rapidly suppressed as heretical. Using the CASTEMO data collection framework, we encoded depositions from the register of the Dominican inquisition of Bologna (1291–1310) and projected them into a network of dissident interactions comprising 328 persons and 1,287 ties. The network is sparse (density 0.024) yet fairly centralized (Freeman's degree centralization 0.41), and dissident ministers display significantly higher degree and betweenness centrality than supporters. A counterfactual node-removal test shows that removing the 20 ministers fragments the network far more (68 components, 42 isolates) than removing the 20 best-connected supporters (33 components, 23 isolates), corroborating the ministers' bridging role; however, the transitivity of the remaining network (0.46) argues against a structure of closed, conspiratorial cliques. Men and women do not differ significantly in degree centrality, gender homophily is moderate (0.21) and balanced between the sexes, and kinship homophily is negligible. Finally, a multilayer exponential random graph model (ERGM) of preaching, resource, communication, contact, and kinship ties, robust to the exclusion of ties reported by ministers, shows that receiving resources significantly increases the likelihood of preaching in return and that kinship promotes resource exchange, supporting the notion of a spiritual–material economy of exchange. We argue that the contribution of SNA reaches well beyond visualization; this method offers a robust and transparent statistical toolkit for answering historical questions. This is a preprint version of a chapter submitted to De Gruyter's "Introductions to Digital Humanities".