eBay: Nero ALEXANDRIA RARE Tetradrachm with SERPENT, Egypt 

   Nero, 54-68 AD, billon tetradrachm of 25.5 mm, 7.20 grams. 
   Struck at the mint of Alexandria in Egypt.
   Obverse: Radiate bust of Nero to right.
   Reverse: Agathodaemon serpent, dated LE.
   REFERENCE: Emmett 106, Year 15.
    
   The light weight of this coin is due to the fact that it was 
   found in the sea and much of the bronze has leached out.