Justinian (527-565), Alexandria, Sear 247: The size the same as thumb-naill. For more details about that coin: http://labarum.info/lbr/show.php?coin=2470 First Justinian; second unknown(probably Justin II); and third Heraclius. - All Alexandrian Constantinople, Antioch and Alexandria were the 3 most important cities in the empire.
I have a cartoonish Justin II of this type. Justin II, CE 565-578 AE 12 nummi, 14 mm, 2.9 gm. Alexandria Obv: DN IVSTNVS PP AV, pearl diademed, draped, cuirassed bust right Rev: Large I-cross-B, mintmark ALEZ. Ref: SB 389, DOC 188
I think you misattributed the coin @TIF. That is not a Justinian coin. Its from the Bozzotian Empire and its an AE 12 dummi of Jesterian II