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Solidus
In the 310s Constantine’s mint settles on a gold solidus of tightly held weight. Silver had already been washed thin.
After silver had been washed thin in the third century, pay tables still needed a piece strangers would trust. In the 310s Constantine’s minting settled on a gold solidus of tightly held weight and fineness — roughly one seventy-second of a Roman pound.
The solidus outlasted the western empire as the Byzantine nomisma. Continuity of weight is the story, not a romance of Rome. The longer page is that gold unit.