| For the first 90 years of the Roman Empire the purity of Rome’s silver coinage was 98% or higher. That standard was kept by emperors Augustus, Tiberius (14-37), Caligula (37-41) and Claudius (41-54), and the first decade of Nero's reign (54-68).
The Great Fire of Rome in 64 marked the start of a debasement that would eventually bring Rome’s silver coinage to unfathomable depths. A pre-reform denarius of Nero, about 98% pure silver. |
 Post-reform denarius of Nero, about 93% pure silver | Nero took the quickest path to raising cash by re-coining old money. Nero decreased the purity of the silver denarii by 5%, dropping it from about 98% to about 93%. At the same time he reduced the weight of the denarius by 12.5%, which further reduced silver content. Nero also reduced the weight of his gold aurei. |  |
 | Nero was overthrown in 68 giving rise to the Year of Four Emperors in 69. Vespasian (69-79), reduced the purity of the denarius to about 90%. In 107 Trajan (98-117) reduced the purity of the denarius to 88%. |  |
 | From there the purity slid until 148, when Antoninus Pius (138-161) removed 5%. The denarius was now about 84% or 83% pure. The denarius reached 71% purity near the end of the incompetent reign of Commodus (177-192) |  |
 | Under Septimius Severus (193-211) the purity of the denarius dropped to about 57%. Over the next four decades, the purity of imperial silver coinage continued to slide, dropping steadily until it had reached about 41% purity under Trajan Decius (249-251). Under Trebonianus Gallus (251-253) and Aemilian (253), it sank to about 35% pure. By 268, the double-denarius had slid to a silver content of 5% or less – in some cases dropping to about 2.5%. |
