Denarius, antoninianus, argenteus, nummus, solidus
Five names come up again and again on our records. Telling them apart by eye is the first skill to acquire, and the quickest.
The denarius and the antoninianus
The denarius is the Roman silver coin par excellence, around three grams and eighteen millimetres, with a laureate portrait. In 215 Caracalla introduced a heavier piece, but not heavy enough to be worth twice as much: the antoninianus, recognisable by its radiate crown.
That crown is a convention: it signals a double value. Across the century the antoninianus loses its silver until it becomes a bronze flan whitened at the surface, and the denarius disappears from circulation.
The aurelianus and the argenteus
Aurelian’s reform of 274 creates an improved coin, which numismatists call the aurelianus, marked XXI in the exergue. Twenty years later Diocletian restores a true fine-silver coin, the argenteus, struck for only a few years and therefore uncommon.
The nummus and the solidus
The nummus is the large silvered bronze of the Tetrarchy, broad and heavy at the outset, then smaller and smaller across the fourth century. It is the most plentiful coin of the end of our period, and often the first one people buy.
The solidus, created by Constantine around 310, replaces the aureus. Struck at one seventy-second of the Roman pound, about four and a half grams, it would remain stable for seven centuries and become the reference coinage of the whole medieval West.