Helena AE Follis, Antioch. 328-329 AD. 

FL HELENA-AVGVSTA, mantled bust right with necklace, wearing ladder-shaped diadem
SECVRITAS-REIPVBLICE, Securitas standing left, lowering branch with left hand, raising robe with right hand. 

Officina letters DE in right field.
Mintmark dot SMANT. 

RIC VII Antioch 82; Sear 16627.

With permission of cngcoins.com, Feb 2014. (attribution
corrected for this diadem type).