Those Old Coins with Holes in Them? - Brown History

Some Greek and Roman overstrikes in the ANS Collection - American Numismatic Society

The Nearly Exhaustive and (Mostly) True History of Challenge Coins

Hadrian 117-138AD - Roman Sestertius For Sale

History of Challenge Coins - Decomil

9 most valuable U.S. coins - InvestmentNews

Various Holed Coins

Bank seeks owner of gold coins cashed for face value – The Denver Post

Currency and Money since the Prehistoric World - Brewminate: A Bold Blend of News and Ideas

Hole-Fillers: What They Are and Why You Should Avoid Them - Numismatic News

ANCIENT LYDIANS WERE THE FIRST TO PRODUCE THE GOLD COIN

Tens of thousands of ancient coins found off Sardinia

Hobo Coins Series II - The Aviator – Dead On Paper