Web is one of the main ways of accessing knowledge in cultural heritage. Recently, several projects in digital humanities have emerged; however only a few are specialized in musicology. In this paper, we present MusicKG, a multilingual knowledge graph about medieval musicology and musical iconography. A specific ontology has been designed to integrate data from several musicology databases such as Musicatallis, Vitrail, or Romane. In addition, MusicKG is connected to the Linked Open Data cloud with a significant part of its classes, properties and instances being linked to Wikidata, Getty, MIMO, ICONCLASS and GeoNames. MusicKG is accessible and reusable by three means: a downloadable RDF dump, a Virtuoso faceted browser and a public SPARQL endpoint. Currently, MusicKG is now used to detect and curate errors and inconsistencies in the original databases. Some representative SPARQL query examples are given to illustrate the scope of MusicKG. We discuss the potential impact on the research work of musicologists and the perspective of facilitating access to this unique cultural heritage.