On 31 October 1941, the construction of Mount Rushmore, an iconic monument with the faces of four American presidents (George Washington, Thomas Jefferson, Theodore Roosevelt and Abraham Lincoln) carved into a mountain of granite, was completed.

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Historian Doane Robinson came up with the idea of creating a place that would praise American history and encourage tourism. Sculptor Gutzon Borglum, the man most responsible for the work, proposed carving the faces of the presidents and began work in 1927.

The site chosen was Mount Rushmore (South Dakota) for several reasons: its height of 1,500 metres, the composition of fine granite that allowed it to be carved, and because it had many hours of daylight to stand out in the landscape.

Borglum planned his work conscientiously. He made several plaster models and, after deciding on one, he took the necessary measurements and marked the precise places where the holes had to be drilled. He then transferred the measurements to the mountain, which was 12 times larger in scale.

The work took 14 years and involved nearly 400 workers. The first phase involved shaping the surface of the mountain and using dynamite for controlled detonations at strategic points. In total, about half a million tonnes of stone were disposed of.

In the second phase, the huge 18-metre busts were carved. The workers, almost all of them experts in stonemasonry and mining, spent hours suspended by ropes and harnesses at a height of more than 70 metres. They used heavy tools such as pneumatic hammers and drills.

Giving expressiveness to the faces on such a scale was a challenge that required a masterly touch: Borglum gave the eyes a sparkle of life by carving a half-metre granite column into the pupils. In this way, the sunlight forms a play of light and shadow, creating a more realistic look.

Gutzon Borglum did not get to see his completed work as he died a few months before completion. It was his son Lincoln Borglum, who was a teenager at the time, who oversaw the final work on the painting.

Behind the heads of the four presidents hides a little secret that almost no one knows about: a secret chamber known as the Hall of Records, which contains a sealed box. It is not accessible to the public, as it is close to the cliffs and dangerous.

The maintenance of the monument is a challenge for the conservators, as it is necessary to climb the mountain to clean the sculptures and remove lichen. In 2005 it was the first time in the monument’s history that it was cleaned with pressurised water.

There is some controversy surrounding the Mount Rushmore monument, as it is located in the Black Hills, which originally belonged to the Sioux tribes. Today there are Indian tribes who claim that it is a sacred site and see it as a symbol of injustice.

Since its opening, Mount Rushmore has been one of the most popular tourist attractions in the USA. Each year it receives an average of 3 million visitors.