The distribution of the black rat (Rattus rattus) has been heavily influenced by its association with humans. The dispersal history of this non-native commensal rodent across Europe, however, remains poorly understood, and different introductions may have occurred during the Roman and medieval periods. Here, in order to reconstruct the population history of European black rats, we first generate a de novo genome assembly of the black rat. We then sequence 67 ancient and three modern black rat mitogenomes, and 36 ancient and three modern nuclear genomes from archaeological sites spanning the 1st-17th centuries CE in Europe and North Africa. Analyses of our newly reported sequences, together with published mitochondrial DNA sequences, confirm that black rats were introduced into the Mediterranean and Europe from Southwest Asia. Genomic analyses of the ancient rats reveal a population turnover in temperate Europe between the 6th and 10th centuries CE, coincident with an archaeologically attested decline in the black rat population. The near disappearance and re-emergence of black rats in Europe may have been the result of the breakdown of the Roman Empire, the First Plague Pandemic, and/or post-Roman climatic cooling.

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The importance of fish for the medieval and early modern economy in the Baltic Sea is known through separate studies by historians and archaeologists. This article aims to combine zooarchaeological data with account books from castles in Kastelholm (Åland Islands) and Raseborg (south-western coast of Finland) in order to understand the processing and transport of fish in the area. Fish was paid as tax by the peasants but was also fished by the castle fishermen and brought to the castles to be consumed there. Here, the preserved fish products are primarily studied through pike and cod, which represent the main economically important larger fish species in the Baltic Sea. The study reveals some differences between the castles studied and the importance of fish for the castle economy.