Antoninianus

The Antoninianus, or radiate, was a coin used during the Roman Empire thought to have been valued at 2 denarii . It was initially silver, but was slowly debased to bronze with a minimal silver content. The coin was introduced by Caracalla in early 215, and was a silver coin similar to the denarius except that it was slightly larger and featured the emperor wearing a radiate crown, indicating that it was a double denomination. Antoniniani depicting females, usually the emperor's wife, featured the bust resting upon a crescent moon.

Even at its introduction the silver content was only equal to 1.5 denarii. This helped to create inflation: people rapidly hoarded the denarii (see Gresham's law), while both buyers and sellers recognised the new coin had a lower intrinsic value and elevated their prices to compensate. Silver bullion supplies were running short since the Roman Empire was no longer conquering new territory, the Iberian silver mines were exhausted, and a series of soldier emperors and usurpers needed coin to pay their troops and buy their loyalty. Each new issue of the Antoninianus thus had less silver in it than the last, and each contributed to ever-increasing inflation.

In 271 Aurelian increased the average weight of the Antoninianus. This was carried out for a short time. This period was also when the enigmatic 'XXI' was first marked on the reverse of the Antoninianus. The true meaning of this series of numbers is still a topic of debate, but it is thought to represent a 20:1 silver ratio (4.76% silver, which may originally have been 5%, if silver enrichment on the surface which has been worn away is allowed).

By the late 3rd century the coins were almost entirely made of bronze from melted down old issues like the sestertius. Vast quantities were being minted, with a large proportion of the stocks being contemporary forgeries, often with blundered legends and designs. Individual coins were by then practically worthless and were lost or discarded by the millions.

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