George Washington letter smashes auction record
The sale, at Christie's in New York, was a record for a letter written by Washington.
The four-page letter was written in 1787 to the president's nephew, Bushrod Washington, and urges adoption of the country's new constitution.
A partially written poem by Edgar Allan Poe sold for $830,500 - a record for a 19th Century literary manuscript.
'Power of the people'
Christie's said the Washington letter had been owned by descendants of Bushrod Washington for more than 100 years. The buyer was not identified.
The previous record for a letter by George Washington was $834,500 (£506,200) in 2002.
In this latest auctioned letter, Washington tells his nephew - who was to be a delegate in the Virginia state ratification convention - that the two-month-old constitution was the key to uniting the newly independent territories.
"The power under the Constitution will always be with the people," he writes.
Also under the hammer at the Rockefeller Center was a rare copy of Edgar Allan Poe's first book, which sold for another record of $662,500.
It was the highest price ever paid for a 19th Century book of poetry, auctioneers said.
Only 12 copies of the 40-page volume Tamerlane and Other Poems, published in 1827, are known to exist.