I just got this Leo I, it is very nice for the type, with a full obverse legend and a sharp portrait. The mintmark is not clear, maybe an O in the exergue, which would indicate the Constantinople mint; but RIC does not list this obverse legend from that mint.
Leo I
A.D. 457- 474
12mm 1.1gm
DN LEO PERPET AVG; pearl-diademed, draped and cuirassed bust right.
REV: Emperor standing facing, head left, holding long cross and placing left hand on head of kneeling captive.
Uncertain mintmark
