You should make an offer

Sotheby says the offer should be between $15 and $20 million. What will you be bidding on? An extremely rare original copy of the American constitution, signed in 1787 in Philadelphia. 

It is one of only 11 known surviving copies and will be sold in New York in November, the auction house said.

It was signed on September 17, 1787 at Philadelphia's Independence Hall by America's founding fathers, including George Washington, Benjamin Franklin and James Madison and ratified the following year. 

Sotheby says, "This was probably printed in an edition of 500 copies. Now only eleven are known to survive and this is the only one in private hands." 

The document is in excellent condition and currently belongs to American collector Dorothy Tapper Goldman.