the engraver gave Jupiter a reversed spear instead of the normal sceptre
Diocletian
A.D. 286
Ӕ Antoninianus 21x22mm 3.8g
IMP C C VAL DIOCLETIANVS P F AVG; Radiate, draped and cuirassed bust right, seen from rear.
IOVI CONSERVAT AVGG; Jupiter standing left, holding thunderbolt and leaning on reversed spear; A in right field.
RIC Vii Lyon 43 variation