Stowaways: Maritime ecology of the oldest commensal ship rats (Rattus rattus) found on a Mediterranean shipwreck

•Oldest known ship rat infestation of an antique Mediterranean sailing vessel.•Ecology of commensal ship habitats explored through zooarchaeology, palaeogenetics, and biometry.•Size estimates for these ship rats suggests some degree of gigantism.•Evidence for Plague of Justinian absent from this assemblage.•Habitat selection, source–sink dynamics have implications for ship rat maritime mobility.