The Mapping Manuscript Migrations (MMM) project was funded from 2017 to 2020 by the Digging into Data Challenge of the Trans-Atlantic Platform. The project partners were the University of Oxford, the University of Pennsylvania, Aalto University, and the Institut de recherche et d'histoire des textes. The project's goal was to bring together data from different sources relating to the history and provenance of medieval and Renaissance manuscripts, enabling large-scale browsing and searching through a semantic Web portal as well as by direct access to the data. Three separate datasets covering more than 200,000 manuscripts, were combined into a unified knowledge graph, using Linked Open Data technologies. This approach includes a unified data model which is based on the CIDOC-CRM and FRBRoo ontologies, as well as more than 20 million RDF triples. Overlapping vocabularies for persons, places, and organizations in the source datasets were reconciled against identifiers from VIAF, GeoNames, and the Getty Thesaurus of Geographical Names. Works and manuscripts were reconciled by semi-automatic matching techniques based on string similarities. The three source datasets were: (1) Schoenberg Database of Manuscripts from the Schoenberg Institute for Manuscript Studies, University of Pennsylvania; (2) Bibale database from the Institut de recherche et d'histoire des textes (IRHT-CNRS, Paris) and (3) Medieval Manuscripts in Oxford Libraries catalogue from the Bodleian Libraries, University of Oxford. To test and demonstrate its usefulness, the MMM Knowledge Graph is in use in the MMM Semantic Portal. Based on the Sampo-UI software developed at Aalto University, the portal enables browsing, searching, and filtering across the project's triple store, together with map-based visualizations of the results.