Although I have been told that our word 'cat' comes from the Roman word for dog, the OED states it is a "common European word of unknown origin". That's my dad's OED, the huge mimeographed condensation of the complete work, which you have to read with a magnifying glass. It's some years old now, but essential, especially when your own Shorter Oxford is missing A-M.
Just don't drop it on your foot.
There is a Latin word catulus, which means puppy. I suppose it's conceivable that a cat might be referred to by a word that indicates 'small dog'. Online sources claim 'catta' as the Latin word. Apparently, it appears in Martial (c75CE). It doesn't, however, appear in my Latin dictionary. It's the Pocket Oxford, second edition, first published 1913. Do I need to upgrade it? Are there new Latin words? (Let's bear in mind that I only bought the new Shorter Oxford English when a) it was on sale and b) I got fed up of not being able to find words like dyslexia.)
It occurred to me today that cats are increasingly popular as pets despite being largely redundant in terms of their (presumed) original purpose. Whether we brought them to live with us so they could kill the rodents that destroyed our crops, or they came to live with us because we attracted the rodents they wanted for food, we'll probably never know. Maybe they just wanted to warm themselves at our fires. It doesn't help that some 180,000 irreplaceable Egyptian cat mummies were sold as fertiliser in the C19th. Priceless information about the origins of the domesticated cat, used to grow crops that their descendants would presumably guard.
I often hear of farmers who have two types of cat. The indoor cats, which are fed and taken to the vet, and the farm cats, which take care of themselves. Perhaps this split has always existed in farming communities and wherever grain is stored: cats that are pets, and cats that work for a living. Perhaps cats hunted in the granaries of the Roman legions, and aren't mentioned simply because everybody would expect them to be there, as common as the air we breathe.
There's a book I'd love to own, The Domestic Cat in Roman Civilization, that might answer the question of the military cat. Unfortunately, it hasn't got past my wishlist.
Which brings me to the question, how much do you need to know to write your Roman novel? Does it matter if you put cats on your farm, in your granary, in your character's house? It does seem entirely possible that the ancient Romans weren't fond of cats as pets. If you're keeping pet birds, of which the Romans kept many, a cat is likely to cause problems.
I think I must have been aware of the unpopularity of pet cats among the Romans when writing early drafts of my novels, because I gave specific reasons why the protagonist's family estate is overrun with cats. His mother is from Egypt, where of course cats were revered, and has introduced them. I feel safe!
And ponies? Next time :).