Yup, definitely late Roman Empire, post-Constantine-the-Great. You can read ...NSTAN... to the left of the portrait, which could be either Constans or Constantine II. Unfortunately, it's the only legible marking I can read on that coin - I can't even find the exergue-line on the reverse to have a crack at the mintmark.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis