Solidus of Constantine

A solidus struck in 320 AD at the Ticinum mint. Diameter 19 mm, 4.38 grams. This gold coin, introduced by Constantine I, was struck at 72 to a Roman pound (libra) and was called "nomisma" in the Greek-speaking eastern part of the Empire——a term derived from Aristotle's teaching that money exists not by nature but by law or custom (nomos). Its nominal fineness of 24 carats was maintained for approximately seven centuries, and the economic historian Lopez dubbed it "the dollar of the Middle Ages."