Today I saw in a museum a row of coins minted by Roman emperors. The last four coins were of the follis kind, belonging to Constantine the Great, Constantius II, Anastasius and Justinian I. .
The picture I took is not very good but one things is clear: the latter two coins (the Byzantine) are much larger than the former two (the Roman).
Is there a pattern here or just a coincidence?
Perhaps the relative value of the follis with respect to other denominations has changed and so its size had to change too? Or is there some arcane numismatic reason for this?