This paper presents the Mapping Manuscript Migrations (MMM) system in use for modeling, aggregating, publishing, and studying heterogeneous, distributed premodern manuscript databases on the Semantic Web. A general “Sampo model” is applied to publishing and using linked data in Digital Humanities (DH) research and to creating the MMM system that includes a semantic portal and a Linked Open Data (LOD) service. The idea is to provide the manuscript data publishers with a novel collaborative way to enrich their contents with related data of the other providers and by reasoning. For the end user, the MMM Portal facilitates semantic faceted search and exploration of the data, integrated seamlessly with data analytic tools for solving research problems in manuscript studies. In addition, the SPARQL endpoint of the LOD service can be used with external tools for customized use in DH research and applications. The MMM services are available online, based on metadata of over 220 000 manuscripts from the Schoenberg Database of Manuscripts of the Schoenberg Institute for Manuscript Studies (University of Pennsylvania), the Medieval Manuscripts in Oxford Libraries, and Bibale of Institut de recherche et d’histoire des textes in Paris. Evaluation of the MMM Portal suggests that the system is useful in manuscript studies and outperforms current systems online in searching, exploring, and analyzing data.