Helena follises are rarer and more interesting, the presented coin has a rarity of R1.
Roman Imperial
Helena Augusta (325-329, mother of Constantine), Follis circa 328-329 AD, Siscia mint
Obverse: diademed, mantled bust right, wearing necklace
FL HELENA AVGVSTA
Reverse: Securitas standing left, lowering branch in right hand and raising hem of robe with left. Mintmark ЄSIS double-crescent
SECVRITAS REIPVBLICE
Weight 2.66 g