obv/IMP C MAXIMIANVS PF AVG; laureate, cuirassed bust left, spear over right shoulder, shield on left arm
rev/GENIO POPVLI ROMANI
Struck in Londinium, c.300 AD. Unlisted in RIC, but Cloke/Toone 2.01.009 (this coin)
There's so much I love about this coin -- the sharp full strike from fresh dies, the lovely London/western mint style, and the way that the irregular flan gives the coin a cameo appearance which is enhanced in hand by the silvering that remains in the fields.
This appears to be, based on RIC, the earliest left-facing bust from the Londinium mint. Cloke/Toone unearthed another that is not listed in RIC, a left-facing consular bust in Diocletian's name (2.01.005), presumably from Diocletian's consulship in 299. I would suggest that this coin is a companion from the same issue, with the elaborate left-facing military bust a complement to Diocletian's consular bust.