It looks like a coin from the Byzantine emperor, Justinian I, 527-565 AD (b.482 / d.565). I think the letters on the reverse side, below the M, says NI?, meaning NIK, having been struck in Nicomedia. I am no expert so I am taking a stab when I say that it is 1 follis, equal to 40 nummi (copper). The M is the Greek alphabetic equivalent of the number 40























