ORC8644 Very puzzling square coin VF

     Julia Mamaea, Æ18x20, Deultum, Thrace, (5.31g) IVLIA MA MAE AVG
     Diademed and draped bust right. / Winged child. Apparently
     unpublished. Puzzling. VF, olive patina. The obverse seems to
     have been struck from a denarius die. Why was a square flan used?