How much is a denarius worth in today's US dollars?
This question is meaningless. Why? 1) The value of the denarius was clearly subject to inflation, and so varied greatly. You could say "how much was the denarius worth of October 1st, 10 AD?", but that value would have changed by the next day. In fact, around the time this edict was proclaimed, clearly the value of the denarius was inflating rapidly. 2) The only way you could come up with a relative value for even on…
However, while this seems to be the view of most economists, I think it's meaningless to ask even what the value of a dollar 50 years ago was, because we are so much richer now. A dollar now can buy you computing power that would have been unthinkable then, cures for diseases that were then incurable, and so on. Economists deliberately ignore immensely valuable new innovations till their prices stabilize (= decline dramatically), since otherwise the CPI would jump around wildly. But this means the CPI greatly understates the growth in wealth.