Dealing with the Heterogeneity of Interpersonal Relationships in the Middle Ages. A Multi-Layer Network Approach

Investigating the case of the Investiture Struggle in the diocese of Cambrai–Arras (c. 1100), this article aims at exploring some crucial issues for historians using social network analysis in the study of heterogeneous relationships. The study proceeds along three lines of enquiry. First, by establishing a hierarchy in the different types of relationships mentioned in the sources, it determines which of them are the most important to model and understand the structure of the network. Second, it demonstrates it is unnecessary to consider co-witnessing relationships (i.e. to be witnesses of a same charter) in the modelling of networks. Indeed, co-witnessing relationships do not help to improve our understanding of the structure of the parties at stake in a conflict. Finally, this paper deals with the importance of rank order in the witness lists. It demonstrates that, in the case of Cambrai, rank order does not have an influence on the global structure of the network. In other words, all individuals in the same witness list play a similar role in the network in terms of party structuring.