The Romans had domesticated snails which they brought to Celtic Briton. They require a very specific chalky, high in limestone soil. They don't really stray from the habitats that were artificially constructed in Briton, so these are usually found exactly where the Celts or Romans placed their ancestors. There is evidence that the ancient Celts kept deer as pets, a very limited practice. Romans attempted to keep some in pens in Roman Briton. Full domestication is unproven, possibly just tamed. Cassius Dio records that war elephants were brought to Celtic Briton. The "questing beast" of Arthurian legend matches the description of an elephant. Celts were talking about elephants centuries after their first arrival. So either these elephants made a tremendous impression (they were meant to) or a population of them was left there. Though it is commonly assumed Normans and/or Saxons brought rabbits to Briton. It may have been the Romans. The Romans probably brought white cattle, guinea fowl, chickens, rabbits, domestic cats, and snails (mentioned above). Note that elephants left no physical evidence; just Cassius Dio's report and the tale of the "questing beast". It was officially illegal in the Roman for non-nobility to own domestic cats. But it still happened, and Briton was a long was from Rome. Of course there were stray cats . Please check my limited facts PS: corraled > corralled civilisations > civilizations