Fallow deer are not native to Britain. Their natural range centres on Anatolia and the eastern Mediterranean, and everything further west is the result of people moving them.
Zooarchaeological work combining ancient DNA, radiocarbon dating and isotope analysis of teeth has resolved a long-standing puzzle. Fallow deer were present in Roman Britain, including animals kept at high-status sites such as Fishbourne, but the isotope and genetic evidence indicates they were brought in rather than locally bred at scale, and no continuous population survived the end of Roman administration. A second introduction in the eleventh and twelfth centuries, associated with Norman deer parks, founded the population that persists.
The episode makes fallow deer an unusually good tracer of human movement, since each translocation leaves a datable genetic and chemical signature. Precisely which eastern Mediterranean source populations supplied each wave, and how the Roman animals were transported, are still being narrowed down.