Looking for any more info on this. Closest I found was a listing on the Wildwinds site that mentioned a mule with a reverse of Severys Alexander. (RIC 100 - "P M TR P VIII : COS II PP" Libertas standing left, holding pileus & sceptre Reka Devnia p137). That doesn't seem to show the altar apparent in the lower left of the reverse though. It's also possible that the previous owner is wrong on the Maximinius ID - the obverse legend is rather blotto. This seems to show the emperor making sacrifice, as seen on several Severys Alexander denarii, but this piece appears to be a Follis.
It looks like Severus Alexander (222-235) who used the legend IMP CAES M AVR SEV ALEXANDER AVG on some coins. It is not a Maximinus Thrax and there is no emperor spelled "Maximinius" (the last "i" is incorrect).
It would not be a follis (not invented until the time of Diocletian). We don't know the weight and size. Could be an As or Sestertius.
..while it does look like it spells 'Maxx' to the eye, it isn't any Max i know of in the portrait..it'd be a safe bet to listen to @Valentinian ....and @ancient coin hunter is correct about the follis...
You coin of Severus Alexander is from 227 AD, the reverse is P M TR P VI - COS II P P and, as you noticed, depicts the emperor with a patera, sacrificing at an altar. It could be a sestertius (RIC 468), a dupondius (469 ) or an as (470), depending on the size and weight. Since nothing on the coin matches the envelope, the most likely explanation is that an earlier owner accidentally switched envelopes and the seller probably didn't know much about ancient coins.
Yes, it appears to be a testing mark IMO Then again, there's a lot of chances to drop the coin on a sharp edge or drop a tool on it between the date of its mounting and when it came into my hands last week.
Your coin uses the same obverse as my sestertius below but my guess is that yours is an as (around 10g?). Mine has a different reverse. Later coins of Severus Alexander used a shortened obverse legend dropping CAES M AVR which is clear on your coin. My guess is that the cheek mark is damage (possibly from a shovel when the metal detectorist was digging it up).
The entire fabric/design of the coin does not look like it came from the late 3'rd - early 4th centuries AD. I agree, it is likely Severus Alexander.
