Mapping fields using co-citation information is a common endeavour in many disciplines but has rarely been performed in the humanities. In this article, I use data from 417 back-of-book source indices to map the field of ancient Mediterranean religion on three levels: sub-discipline, ancient work, and references in ancient works. The method innovatively makes use of primary text references, rather than research articles, to construct the co-citation network. After mapping the overall relationships between sub-disciplines, I show how the data can be used to identify two types of ancient works that bridge these sub-disciplines: works which are central for the whole network, and works which are not central overall but cited more often with specific sub-disciplines. The article provides an understanding of the structure of the field of ancient Mediterranean religions, and more generally on the challenges and advantages of methods to map scholarship in historical disciplines.