The Follis

The Roman follis was a large bronze (or billion) coin  introduced in about 294 with the Diolcetian reformation of the coinage It weighed about 10 grams and was about 4% silver, mostly as a thin layer on the surface. The word follis means bag (usually made of leather), and there is evidence that this term was used in antiquity for a bag containing a specific amount of coins. The follis of Diocletian, despite efforts to enforce prices was revalued and reduced. By the time of Constantine, the follis was smaller and barely contained any silver.