Follis is certainly wrong - this was the
Roman name for a *bag* of coins of value 12,5000 "
denarii communes" (i.e.
denarii at a time when it was just an accounting unit, no longer an actual coin
denomination). I'm not sure who introduced the incorrect modern usage of this name.
The name
nummus is probably the best. There are
contemporary references to this name being used for the bronze/billion coinage at the time of Diocletian's monetary reform, and the same name appears to have
still been in use at least as late as c.321AD
per reference to this coin's (
nummus) value being halved, apparently in reference to a revaluation that occurred at the time Licinius introduced
new coins marked "12 1/2" [
denarii communes].
The issue of denominations/naming is complicated by Constantine's coinage reform of c.318AD when (
per modern testing) he significantly increased the silver content of the bronze/billion coinage (from 1-2% to 4-5%), and reintroduced older
reverse types associated with a higher yet (20%) silver content. Presumably
per the increased silver content (and intended value association), this coinage reform increased the value (tariffing) of the bronze/billion coinage, and the question then becomes whether the
denomination name stayed the same (
nummus), or changed.
Given the apparently (c.321AD) post-reform use of the name
nummus, it seems the safest guess is that the name
nummus persisted after Constantine's c.318AD reform, but others have suggested that the
denomination name changed and have equated this to the known "
centenionalis" of this approximate time. The competing theory is that the "
centenionalis" instead refers to a slightly later
denomination introduced after Constantine's death.
Ben
