Here is an interesting unofficial overstrike. It is an IOVI undertype, which was issued A.D. 313- 315. This type was demonetized after the monetary reform in A.D. 318, which introduced the VLPP in bronze. Normally, the unofficial VLPP are circa 17-18mm, close to the official issue; but this coin, struck on an IOVI flan is almost 22mm. So, because of the size and crude overstrike, everyone would have known that this was unofficial, but it seemed it was more important to at least attempt an overstrike, rather than continue to circulate an unaltered IOVI.
It looks like the undertype is Siscia 7 (third picture below)
IMP CONSTANTINVS AVG; laureate head right.
IOVI CON-SERVATORI; Jupiter standing l., chlamys across l. shoulder, leaning on sceptre and holding Victory on globe in r. hand; eagle with wreath to l. on ground; in right field ?.
in ex. SIS
The CNG description--
"Constantine I. AD 307/310-337. Æ Follis (21.5mm, 4.06 g). Contemporary imitation. Uncertain mint in the Danube basin. Struck circa AD 320s. Helmeted and cuirassed bust right / Two Victories standing vis-à-vis, holding inscribed shield on altar. Overstruck on an a Siscia mint follis of Constantine I. Sergeev 232-7. For undertype cf. RIC VII 3 (Siscia). Green patina. In NGC encapsulation 4530021-005, graded Ch AU, Strike: 3/5, Surface: 3/5, light smoothing. Remarkably clear undertype. Very interesting"
