"Nummus" or "nummion" is the Greek for "small coin." In the Byzantine Empire a nummus was worth a fortieth of a follis, the standard copper coin of the period. In the 6th century there were 180 folles to a solidus. The value of these copper coins were usually indicated on the reverse, generally in Greek letters used as numerals, but sometimes also by Roman numbers, as on this coin. The four strokes following the Roman number indicate the year of issue, i.e. the fourth year of the reign of Phocas, or 605-606 AD.