Bought this mostly for the error, though it's a neat reverse. (Cista mystica, IIRC?)
Seller said this was Caracalla. I dunno. Only Roman emperor I could recognize on a coin is Septimius Severus.

17 mm, 2.63 grams.
Not really visible on the photo: the area where the die ran out is more than twice as thick as the rest of the coin.
[EDIT: added ID to title. Or tried to, anyway.]