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Constantine I AE follis AD 306-337, Heraclea.
Obv: CONSTANTI-NVS MAX AVG, rosette-diademed, draped, cuirassed bust right.
Rev: D N CONSTANTINI MAX AVG around VOT XXX within wreath.
Mintmark dot SMH Delta.

RIC VII Heraclea 94, 
very rare, rated R5.

Corrected.
The seller, AAH, not only got the obverse legend and bust
type wrong, but also the mintmark, so the rarity they
cited was incorrect and someone got a very rare coin for
under £2 !