New ancient DNA analysis has shed light on how the black rat, blamed for spreading Black Death, dispersed across Europe — revealing that the rodent colonized the continent on two occasions in the Roman and Medieval periods. By analyzing DNA from ancient black rat remains found at archaeological sites spanning the 1st to the 17th centuries in Europe and North Africa, researchers have pieced together a new understanding of how rat populations dispersed following the ebbs and flows of human trade, urbanism, and empires.