BIRMINGHAM, England — An amateur historian believes he has unearthed a letter written by the President Lincoln — after buying it for $1.89 at a parking lot sale.

Kenneth Anderson-Jones, 75, found the dusty and dirt-encrusted framed document in a pile of bric-a-brac at the sale near his home in Stratford-upon-Avon.

When he got it home, he cleaned it up to find it was a letter written in 1856 by Lincoln giving Lieutenant General Ulysses Grant total command of the American army, a move that led to victory in the American Civil War.

Yesterday, his nephew took the letter to Sotheby’s to have its authenticity checked. The American Library of Congress, which keeps official documents, said it did not hold a copy of the letter and was keen to examine Mr. Anderson-Jones’s find.

The document, dated March 10, 1864, commissions Grant as lieutenant general and was presented to him by Lincoln.

Only George Washington and Winfield Scott had held the rank before Grant.

With this appointment, Grant became “general in chief of the Army and answered only to President Lincoln as commander in chief.”

The instruction pre-empted the end of the civil war, which ran between 1861 and 1865.

A spokesman at the Library of Congress said: “According to our official collected records of Abraham Lincoln, the original of this letter has never been found.

“Lincoln did write copies of his important letters and speeches, but it would be unlikely he would do this with a military document.”