AE Quinarius (Billon Quinarius)

There actually is no such denomination as the "AE Quinarius" (plural: "Ae Quinarii"), because the coins to which it applies are actually a special sort of the "AR Quinarius", or silver quinarius, denomination.   The coins called "AE Quinarii" are actually silver quinarii which were debased to such an extent that they are low-grade billon with a bronze appearance.  "Ae" comes from the Latin noun for bronze or something made of bronze, "aes".  "Quinarius" originally meant "containing five" and was thus applied to the small Republican silver coin which was half the value of the denarius, which was originally valued at 10 asses (meaning its half, the "quinarius" was valued at 5 asses).  The names "AR Quinarius" and "AE Quinarius" are necessary rather than simply "quinarius", because there were also gold quinarii (see "AU Quinarius") struck as the half of the aureus.

The silver coinage of the Roman Empire ceased to circulate within fifty years of the introduction by Caracalla in 215 of the antoninianus.  However, neither the antoninianus, denarius, nor the "AR Quinarius" were officially discontinued at that time (about 260), they simply were debased to the point at which they appeared to be bronze coins (although in reality being base billon containing 4% silver).

The "AR quinarius" was never a common denomination, and became even less so after the debasement in its "AE Quinarius" form.  However they were minted up until the time of Diocletian's reform of 294, when high-fineness silver coins were re-introduced as "argentei" (see "Argenteus").  Thus the term "AE Quinarius" only applies to the billon quinarii minted between about 260 and 294.

The obverse of the "AE Quinarius" was the laureate bust of the emperor, except for an enigmatic issue of the British usurper Allectus (see below).  It weighed about 1.75 grams and its diameter was 13-14 millimeters, again with the exception noted below.

The illustrated coin is a reverse of an interesting Ae Quinarius of Allectus, a usurper in Britain who maintained himself from 293-296.  In the latter part of his reign he began to issue these coins, which all bear the initial letter "Q" in the exergue regardless of the mint.  It is believed that this is the denominational mark for "quinarius".  These coins, at 2.7 grams, are slightly over half the weight of Allectus' normal "antoniniani" (or sometimes called "aureliani" at this time).  It is believed, based upon the Aezani inscription of 301 AD, that Aurelian had re-valued the antoninianus at four denarii instead of its original two.  A unique feature of Allectus' quinarii is the obverse radiate bust (a radiate bust usually denoted a "double" denomination in the Roman coinage system, not a half).  However, assuming the break-away British empire, formed only 12 years after Aurelian's death in 275, continued the coinage system laid down by Aurelian, Allectus' quinarius, although half of the normal value of the antoninianus or aurelianus, was still worth two denarii, and thus Allectus may have justified the radiate bust.  Since the name "quinarius" had over the centuries lost its original meaning ("containing five") and come to represent a coin that was simply half of another, it was only natural that Allectus' new "half" should be called a quinarius.  When Constantius I re-established central Roman rule over the British islands in 296 AD, the unique radiate quinarius was discontinued.