Arguably one of the most popular type issues by any Roman empress, Otacilia Severa's Hippopotamus coinage highlight the gaiety of Rome's spectacular Secular Games to mark the 1,000th anniversary from her founding by Romulus. Surely it was no easy feat to capture and transport such a fantastic beast from the depths of Africa all the way to the Colosseum in Rome! Outwardly, this appears to be a regular old, fairly low grade Hippo sestertius, except for one problem - it is 24mm across and weighs only 6.67g. (Yes, I know my scale is dusty) As the Secular games were designed to distract the public from the ongoing financial and military crisis, large number of sestertii and a limited number of middle bronzes were minted, the latter being likely used as donatives for the crowd as the denomination had been largely defunct since the middle Severan period. Which brings me to my point - I cannot find either a reference for this coin as an as, nor another example. The tag included with this coin describes it as a sestertius with a chipped edge, but the loss of 6mm off the diameter cannot cause this coin to shed about 50-75% of its original weight. I feel that beyond a doubt this coin was struck on a planchet intended for an as. But whether this is an as struck with sestertius dies, or a potentially unpublished type - I'm not sure. This isn't an area of Roman numismatics I know particularly well - I'd welcome insights!
An as of this period should be closer to 10-12g. so 6.67g seems light. I have seen asses of Otacilia but do not recall a hippo. However, a search turned up a lighter one so it would seem your coin could possibly be OK (and rare). https://www.acsearch.info/search.html?id=4436363
I have six sestertii from the reign of Philip I. Their weights are 15.11 g, 19.61 g, 11.52 g, 17.45 g, 14.33 g, and 19.43 g. I have two aes, weighing 8.81 g and 7.18 g. Your impression that the coin is severely underweight is accurate. The British Museum only has sestertii with this reverse type, weighing 18.84 g and 16.44 g. RIC, Sear, Hunter, Cohen, and Wiczay do not note middle bronzes with this reverse type. Rather, the middle bronzes with the SAECVLARES AVGG reverse type have a cippus, not a hippo. Your coin looks genuine, but struck on a small module. I think your explanation of struck on the wrong flan is as good as any. Here's my humble example: Otacilia Severa, AD 244-249. Roman Æ sestertius; 11.52 g, 30.4 mm. Rome, AD 248. Obv: MARCIA OTACIL SEVERA AVG, diademed and draped bust, right. Rev: SAECVLARES AVGG SC, Hippopotamus standing right. Refs: RIC 200; Cohen 65; RCV 9170; Hunter 26.
..seems a lil low on weight, but still a crowd pleaser. .Otacila Severa/ pachyderm sestertius. 27mm, 21.13gms Rome mint 248AD
Thanks all, and lovely coins! Taking another closer look at mine, I am increasingly leaning toward it being the ancient equivalent of a "wrong planchet" error.
Interesting discussion. The late sestertii (and smaller AEs) are confusing to me. The weights seem to be all over the place starting around the time of Commodus. I have a Septimius Severus dupondius that is tiny compared to an Elagabalus as, etc. Here is my only SAECVLARES sestertius - Philip with an antelope. At 13.59 grams it seems to barely qualify as a sestertius. Maybe it's not. Philip I the Arab Æ Sestertius (248 A.D.) - Rome Mint IMP M IVL PHILIPPVS AVG, laureate, draped, cuirassed bust right / SAECVLARES AVGG, SC in ex., Antelope walking left. RIC 161a; Cohen 190. (13.59 grams / 28 mm)
24mm diameter corresponds to an area of 1809 mm2, and 30mm diameter corresponds to an area of 2826 mm2. That's 64%, which would mean an original weight of 10.4g. The chipping and corrosion has taken some more metal off too, so an original weight over ~11g is more probable... within the realms of possibility that it was struck on a sestertius flan, then?
The thought did cross my mind, but here is a side by side of this coin versus a sestertius of her husband, from the same lot: The Otacilia is pretty corroded, but the coin would have to be featureless to lose that much metal off the surface. For comparison, there was another OS Secular games As in the lot, and it was the same thickness. I don't think I've ever seen a sestertius from the period that was under 16g. The other as weighed 9.64g for comparison.
RC above notes that he has a sestertius of the period weighing 11.52g, and there are hippo sestertii on acsearch weighing 11.65g, 12.29g, and 12.88g for example. If it was a hard strike that stretched out the flan a lot, perhaps it could end up being that thin, and quite a large diameter so the coin has lost even more than 6mm? It is pretty thin, though, and to my eye the flan doesn't look to have lost so much diameter, judging by that side view... so the hypothesis of an as flan is certainly viable. (Certainly a sestertius die.) A question mark coin, but lots of fun to think about!
This Otacilia sestertius is 21.6g and well made. ...as is this 20.9g Philip I. Later in the reign when the Saeculares coins were made, the weight standards fell. My wolf is dumpy and 13.9g. From the same series, this Tranquillitas is only 11.7g. I call this Decius at 11.2g a sestertius. The diameter and dies are sestertius size but the flan is thin. I have never been able to convince myself of why this coin is light but I have a theory. It is way too big to be an as. This Decius dupondius (radiate crown) is 7.5g and fits the reduced diameter of that denomination. Double its weight would be 15g. and appropriate for a sestertius. Using that theory, this 14.3g sestertius would seem in line with the dupondius above. ...but this 18.1g sestertius seems heavy. ...as does this 17.1g Herennia sestertius. After worrying too much about the matter, I decided that weight standards were not a priority in the Decius mint. The above makes my 32.5g double a reasonable weight even though there are 40g coins. Summery: I don't know. Has anyone published a theory making sens of this other than the 'not a priority' idea? I'll offer this completely unscientific idea. After making bronzes of good weight for the first part of the reign, Philip lowered the standards for the Saeculares coins. Decius took over the reduced standards but soon restored some of the reduction adding his very special double sestertius in the hope of restoring faith in the bronzes. This, along with a good dose of individual flans not being carefully adjusted, leaves us with a wide variation of bronzes which hung on for a short while before pretty much collapsing under Valerian. I have insufficient evidence to call this a theory but I will throw it out there as a guess. Those of you who are interested in weight could study the coins online and see if a pattern emerges or if the idea of 'just careless' makes more sense.
