The legend on it reads DN (Dominus Noster) and the name of the emperor (I think Gallienus but not sure I can read it, who ruled in late third century AD) and then again legends PF AVG (Pius Felix Augustus). That type of legend was only in use since late second century/early 3rd, where emperors were referred to as dominus (lord and master) rather than just princeps.

The type of coin is an aureus, the standard gold coin of the empire for most of its lifespan, later changed to solidus by Constantine the Great.

Source: this is my personal niche obession. But I’m far from a professional numismatist.