Commemorative As struck under Caligula in honor of his grandfather Marcus Agrippa: Online Coins of the Roman Empire: RIC I (second edition) Gaius/Caligula 58 (numismatics.org)
@paschka That's a nice one, by the way. It's got a good portrait of the hard-bitten old general, with his name clearly legible. I like it! They are common coins, but popular with collectors.