I'd be pretty wary about cleaning it, as you can easily damage a coin if you are too harsh, particularly if it was British found (I learned the hard way that when a seller warns you to be gentle with a British uncleaned, he means it. I never knew you could rub off most of the obverse of a coin with a toothbrush). I doubt it's a British uncleaned, since sellers of those are usually pretty specific about it, but if you chose to clean it, you still should be careful not to scratch the thing up by usuing something too hard to scrape it, nor do you want to strip it down to the bare metal with a chemical that's too harsh. You can find a decent guide to cleaning uncleaned ancients
here, and if you really want to use a faster working chemical, you can always pick up one of the Gringott's Mixes (you can find them easily enough online), which are designed to use on ancient coins. No matter what you use, if you are cleaning it properly, it's going to be a long process. There's the additional problem that you may already have a coin that is cleaned as much as it should be, so I would recommend giving us even a blurry picture of the thing to see if we can tell if any cleaning is a good idea.
I also recommend giving us the bits of the legend that you can read. Even if you can only read a few of the letters, we may be able to narrow down what it could be.
Finally, I'm curious as to where you got it and how much you payed. Did you just grab one off of eBay or a local dealer or something? Did they give you any information about it aside from it being Roman?
