Emperor Valentinian Can't for the life of me make out the mint mark. https://www.wildwinds.com/coins/ric/valentinian_I/t.html
You can tell the Emperor's name, by looking at the legend on the obverse. If I add spaces, it says "DN VALENTINIANVS PP AVG". The "AVG" means "Augustus", which was the Emperor's official title. However, I don't know, if it is Valentinian I, Valentian II, or Valentinian III. Probably not Valentinian III, because probably a Valentinian III coin would be cruder, I think.