AU Quinarius (Billon Quinarius)

"Au" is the chemical symbol for the element gold, and the symbol comes from the Latin word for gold, "Aurum".  The term "quinarius", when used for a Roman gold coin of half the weight of the "aureus", is actually mis-applied. "Quinarius" is a Latin adjective which means "containing five" and was originally used to describe the half of the silver denarius.  The denarius originally was equal to 10 asses (see As) and bore the mark "X" to reflect its value.  Its half was therefore worth five asses and thus called a "quinarius".  By analogy the term has been extended to mean the half of the gold aureus, although in no sense does the original meaning "containing five" apply.

The first golden quinarii were struck in the name of Julius Caesar by the moneyer L. Munatius Plancus about 45 BC. They were struck at exactly half of the weight of the Caesarian aureus which weighed 8.19 grams (40 to the Roman pound). Augustus adopted the Republican system when he gained imperium, although Augustus' aurei are usually 7.75 - 8.00 grams in weight and 19-20 millimeters in diameter. His gold quinarii are about 3.95 grams in weight and 14-15 millimeters in diameter.

The distinguishing feature of quinarii, both silver and gold, was the "Victory" motif on the reverse. Nearly invariably "Victory" is featured, although in many different poses and actions.

The weight of the quinarius naturally varied with the weight of the aureus, but through most of the first and second century it was about 3.65 grams. The diameter was relatively constant at about 14-15 millimeters. In the mid-third century the gold quinarius fluctuated greatly and was not struck during all reigns, reflecting the uncertain times.  Finally Diocletian stabilized it in 290 at about 2.7 grams (120 to the Roman pound) and there it remained until it was discontinued about 305 or 306. Another smaller fractional gold piece, the 1½ scripulum (q.v.) was instituted by Constantine I in 310, but the "half" gold unit was not restored until Constantine I issued the half-solidus, or semissis, about 320.