I know that it is getting a little old, but one more classic Byzantine rarity, a sole portrait solidus of Basil I (867-886).  This is one of the more interesting Byzantine coins as it is one of the few to show the emperor in a full length standing position.  There is quite a debate about the origin of this piece and the current consensus is that it was struck for the New Year celebration of 868 and given out during that event.  This could account for the lack of pieces known.  Presently, I can only account for 5 pieces, with only 2 (this being the far better) available in the market place, the others are impounded in museums.  The pedigree of this piece is, Hunt Sale Lot 677.  The coin weighs 4.47g and exhibits the slightest amount of wear or "cabinet friction" on the highest part of the coin. There is also a slight circular indention in the lower right obverse field.