On July 4, 1776, Caesar Rodney sent a letter from Philadelphia to his brother back home in Delaware, mentioning the Declaration of Independence, which he had just signed.

Rodney's letter was sold at auction Wednesday for $440,000, setting world records for the sale of any letter and for an American autograph, Christie's said.Chicago book dealer Ralf Newman bought the letter, addressed to Capt. Thomas Rodney in Dover, Del., on behalf of a private client, the auction house said. It was estimated before the sale that the letter would bring $100,000 to $150,000.

The old record for an American autograph was $396,000 paid in 1987 for a Thomas Jefferson letter, according to Dana Micucci, a spokeswoman for Christie's.