The letter written by renowned physicist Albert Einstein to urge President Franklin D. Roosevelt to develop the first atomic bomb is set to be auctioned off with an estimated value of $4 million.

Penned in 1939, the two-page letter emphasized the need for urgent action in establishing a nuclear program in the United States, citing concerns that Nazi Germany may have been working on similar capabilities.

‘It is conceivable – though much less certain – that extremely powerful bombs of a new type may thus be constructed,’ the letter said.

Although the letter bore only Einstein’s signature, it was actually composed by inventor Leo Szilard, who strategically chose to have it signed by the world-famous physicist to capture the president’s attention.

It is being sold at Christie’s in New York on September 10 alongside a collection of artifacts that belonged to the late Microsoft co-founder Paul Allen, who died in 2018.

Einstein’s original letter is held at the Franklin D. Roosevelt Library and Museum in New York, but the physicist also signed a second letter that he left with fellow scientist Leo Szilard for safekeeping.

In the letter, Einstein and Szilard suggested that a chain reaction of uranium could be turned into nuclear energy that would lead to the construction of ‘extremely powerful bombs.

‘A single bomb of this type … might very well destroy the whole port together with some of the surrounding territory.’

Einstein and Szilard advised the president to ‘have some permanent contact maintained between the administration and the group of physicists working on chain reactions in America.

‘One possible way of achieving this might be for you to entrust with this task a person who has your confidence and who could perhaps serve in an unofficial capacity.’ 

Einstein, who was Jewish, fled to the US from Germany during the Nazi order and sent the letter to President Roosevelt less than a month before Germany invaded Poland. 

Two years after the letter was penned, the Manhattan Project led by J. Robert Oppenheimer was established to build the atomic bombs that were dropped on Hiroshima and Nagasaki in Japan in 1945.

Szilard kept the letter in his possession for the rest of his life, but his heirs sold it off to Malcolm Forbes – a 1996 third-party presidential candidate – for $200,000 in 1986.

‘The letter represents an incredible historical milestone; to me, it is the reason we’ve had peace for 40 years,’ Forbes told The New York Times after he purchased the letter.

Forbes later sold the letter to Allen in 2002 for $2.1 million.

Marc Porter, chairman of Christie’s Americas, told the Wall Street Journal that Allen ‘undoubtedly knew it was one of the most important documents in the history of the 20th century, and that’s not the kind of thing you just hang in your office.’

He said Allen had carefully stored the letter away from sunlight, preserving the artifact.

Jessica Stanley, Christie’s PR director, told DailyMail.com that the letter is in ‘excellent condition’ and is being sold by Allen’s estate in the ‘Gen One’ auction.

This is ‘a series of three auctions of object and art showcasing scientific achievement and technological innovation’ that are all from Allen’s collection.’

Pursuant to Allen’s wishes, all proceeds from the auction will be dedicated to charity.

Under President Roosevelt’s orders, Oppenheimer set up a team of scientists in a remote area of New Mexico to research uranium and build the atomic bomb, but by the time it was tested in 1945, the Germans were already defeated and World War II had begun.

Once the bomb was created, President Harry Truman ordered that the weapon be used to bring the war to an abrupt end.

The US dropped the world’s first atomic bomb on Hiroshima, creating a blast that equated to 15,000 tons of TNT that reduced four square miles of the city to rubble and killed 80,000 people.

In the following weeks, roughly 50,000 people died from shrapnel wounds and radiation poisoning, bringing the total deaths to 140,000.

A second atomic bomb was dropped on Nagasaki three days later, killing 40,000 people and within a few days Japan announced its surrender.

The devastation was so great that no nation has used an atomic bomb since. 

At the time, Einstein thought it was his duty to warn President Roosevelt about the possibility that Germany might create a nuclear bomb after he sought sanctuary in the US and later renounced his German citizenship to become an American.

His discovery of general relativity, also known as the theory of gravity, and being a Nobel Peace Prize recipient for his services to theoretical physics helped Einstein’s transition to the US where he took a professor position at Princeton.

Einstein later regretted penning the letter to Roosevelt because of the role it played in making America the only country to make nuclear weapons at the time.

In a 1947 article titled ‘The Man Who Started it All,’ Einstein said: ‘Had I known that the Germans would not succeed in producing an atomic bomb, I would never have lifted a finger.’