Double Denarius

Higashiyama

The double denarius is often referred to (by present day collectors) as the Antoninianus, after the official name of the emperor "Caracalla" who introduced the coin in 215.

Here is a perhaps naive sounding question: books and articles say that we do not know the name that was used by the Romans of that era to refer to this coin. How can that be? There are a lot of historical sources from that era and shortly after (letters, histories, essays, etc.). Did people not refer to money in their writing? Aren't there, for example, contemporary accounts of the Diocletian reforms, and wouldn't they have made reference to the prior denominations?

1984worldcoins

There are lots of things out in the world that need to be discovered. Just recently, a person very well prepared in recognizing roman artifacts (but not a professional!) discovered that a bust known to represent Marcus Aurelius was, in fact, a bust of Lucius Verus (the bust is situated in a private space). So the issue you describe can be a very interesting project to pursue.
Also, there is a posibility that the coin did not have a name, it was just a 2 denarius coin, like any other modern 2 of any currency coin.

Sapyx

@Higashiyama said:
Here is a perhaps naive sounding question: books and articles say that we do not know the name that was used by the Romans of that era to refer to this coin. How can that be? There are a lot of historical sources from that era and shortly after (letters, histories, essays, etc.). Did people not refer to money in their writing? Aren't there, for example, contemporary accounts of the Diocletian reforms, and wouldn't they have made reference to the prior denominations?

There are plenty of surviving records mentioning money; very very few of them talk about what we consider as "denominations", and none of them mention this specific denomination. Most surviving references to money reference amounts of money, which the Romans at the time reckoned in sestertii as the basic money of account. So if you gave your slave 2 denarii to go and do the family shopping, your written records wouldn't say "2 denarii", they'd say "8 sestertii", there being 4 sestertii to the denarius. You wouldn't have written down the specific coins you gave him.

There are no records surviving from the time of Caracalla about the introduction of the coin we call the antoninianus. It just... appears, with no mention in the histories. We aren't even 100% certain about it's denomination; we assume it's a 2-denarii coin as there had by that time been a long-established tradition that a radiate crown on a coin indicated a double-denomination (the dupondius or 2-asses coin always had a radiate crown) and the antoninianus also consistently has a radiate crown. But we have no records at all saying words to the effect of "Caracalla introduced a coin worth 2 denarii (or 8 sestertii) and it was called a...".

There are likewise no written records of Diocletian's reforms to the coinage; the histories make reference to edicts on taxation and coinage being made but the actual edicts themselves have not survived. All the information we have about the reforms is inferenced and extrapolated from the coinage itself. For example, we know he introduced a new silver coin and it seems to have been called the "Argenteus"; we don't actually know the official exchange rate between the argenteus and the old antoninianus. We have several surviving fragments of copies of Diocletian's futile attempt at fighting inflation, but the prices thereon are all recorded in denarii (which by the 300s seems to have replaced the sestertius as the money of account).

Diocletian introduced (or reformed) the antoninianus into a new, completely-lacking-in-silver coin which was called the "Radiate". But again, we don't know the official exchange rate between radiate, argenteus, and antoninianus. If it was ever written down, no copies of this writing have survived. You can find conversion tables stating, for example, that the argenteus was worth 100 old denarii. But this is just a barely educated guess; no actual evidence of the coin's face value has survived, and the coins themselves unfortunately lack any such mark or indicator of value. One could also postulate that "radiate" might also have been the name of the pre-reform antoninianus, but this was perhaps a nickname at best, especially since other denominations of Caracalla also had radiate crowns, so "radiate" would not have been a particularly useful name at the time the coin was first launched.

The best surviving records regarding everyday coinage and finances from this time period comes form Roman Egypt, and a hoard of scrap papyrus fragments found in Oxyrhynchus. Unfortunately, Roman Egypt did not use regular Roman currency, but its own separate currency system, so there are no mentions of Roman coins or currencies.

On top of all of this, some of the surviving written records have proven to be unreliable. The Historia Augusta, a 5th century compilation of Roman history covering the period AD 117 to 284, names numerous coinage denominations various emperors issued - which sounds great and useful, but none of the recorded coins seem to correlate to any actual coins anybody actually made; it seems the author of the Historia Augusta sometimes just made stuff up and wrote it down. I don't think the Historia mentions any new large silver coin first issued by Caracalla. Other "facts" in the Historia have proven to be equally fabricated, but unfortunately, it is the only surviving history the Romans themselves wrote concerning this time period.

Higashiyama

@Sapyx - thanks for taking the time to write up this fascinating account!