This article was originally posted at The New York Times.

IN the summer of 1916, a young Oxford academic embarked for France as a second lieutenant in the British Expeditionary Force. The Great War, as World War I was known, was only half-done, but already its industrial carnage had no parallel in European history.

“Junior officers were being killed off, a dozen a minute,” recalled J. R. R. Tolkien. “Parting from my wife,” he wrote, doubting that he would survive the trenches, “was like a death.”

The 24-year-old Tolkien arrived in time to take part in the Battle of the Somme, a campaign intended to break the stalemate between the Allies and Central Powers. It did not.

The first day of the battle, July 1, produced a frenzy of bloodletting. Unaware that its artillery had failed to obliterate the German dugouts, the British Army rushed to slaughter.

Before nightfall, 19,240 British soldiers — Prime Minister David Lloyd George called them “the choicest and best of our young manhood” — lay dead. That day, 100 years ago, remains the most lethal in Britain’s military history.

Though the debt is largely overlooked, Tolkien’s supreme literary achievement, “The Lord of the Rings,” owes a great deal to his experience at the Somme. Reaching the front shortly after the offensive began, Tolkien served for four months as a battalion signals officer with the 11th Lancashire Fusiliers in the Picardy region of France.

Using telephones, flares, signal lights, pigeons and runners, he maintained communications between the army staff directing the battles from the rear and the officers in the field. According to the British historian Martin Gilbert, who interviewed Tolkien decades later about his combat experience, he came under intense enemy fire. He had heard “the fearful cries of men who had been hit,” Gilbert wrote. “Tolkien and his signalers were always vulnerable.”

Tolkien’s creative mind found an outlet. He began writing the first drafts of his mythology about Middle-earth, as he recalled, “by candle light in bell-tents, even some down in dugouts under shell fire.” In 1917, recuperating from trench fever, Tolkien composed a series of tales involving “gnomes,” dwarves and orcs engaged in a great struggle for his imaginary realm.

In the rent earth of the Somme Valley, he laid the foundation of his epic trilogy.

The descriptions of battle scenes in “The Lord of the Rings” seem lifted from the grim memories of the trenches: the relentless artillery bombardment, the whiff of mustard gas, the bodies of dead soldiers discovered in craters of mud. In the Siege of Gondor, hateful orcs are “digging, digging lines of deep trenches in a huge ring,” while others maneuver “great engines for the casting of missiles.”

On the path to Mordor, stronghold of Sauron, the Dark Lord, the air is “filled with a bitter reek that caught their breath and parched their mouths.” Tolkien later acknowledged that the Dead Marshes, with their pools of muck and floating corpses, “owe something to Northern France after the Battle of the Somme.”

In a lecture delivered in 1939, “On Fairy-Stories,” Tolkien explained that his youthful love of mythology had been “quickened to full life by war.” Yet he chose not to write a war memoir, and in this he departed from contemporaries like Robert Graves and Vera Brittain.

In the postwar years, the Somme exemplified the waste and futility of battle, symbolizing disillusionment not only with war, but with the very idea of heroism. As a professor of Anglo-Saxon back at Oxford, Tolkien preferred the moral landscape of Arthur and Beowulf. His aim was to produce a modern version of the medieval quest: an account of both the terrors and virtues of war, clothed in the language of myth.

In “The Lord of the Rings,” we meet Frodo Baggins and Samwise Gamgee, Hobbits of the Shire, on a fateful mission to destroy the last Ring of Power and save Middle-earth from enslavement and destruction. The heroism of Tolkien’s characters depends on their capacity to resist evil and their tenacity in the face of defeat. It was this quality that Tolkien witnessed among his comrades on the Western Front.

“I have always been impressed that we are here, surviving, because of the indomitable courage of quite small people against impossible odds,” he explained. The Hobbits were “a reflection of the English soldier,” made small of stature to emphasize “the amazing and unexpected heroism of ordinary men ‘at a pinch.’ ”

When the Somme offensive was finally called off in November 1916, a total of about 1.5 million soldiers were dead or wounded. Winston Churchill, who served on the front lines as a lieutenant colonel, criticized the campaign as “a welter of slaughter.” Two of Tolkien’s closest friends, Robert Gilson and Ralph Payton, perished in the battle, and another, Geoffrey Smith, was killed shortly afterward.

Beside the courage of ordinary men, the carnage of war seems also to have opened Tolkien’s eyes to a primal fact about the human condition: the will to power. This is the force animating Sauron, the sorcerer-warlord and great enemy of Middle-earth. “But the only measure that he knows is desire,” explains the wizard Gandalf, “desire for power.” Not even Frodo, the Ring-bearer and chief protagonist, escapes the temptation.

When Tolkien’s trilogy was published, shortly after World War II, many readers assumed that the story of the Ring was a warning about the nuclear age. Tolkien set them straight: “Of course my story is not an allegory of atomic power, but of power (exerted for domination).”

Even this was not the whole story. For Tolkien, there was a spiritual dimension: In the human soul’s struggle against evil, there was a force of grace and goodness stronger than the will to power. Even in a forsaken land, at the threshold of Mordor, Samwise Gamgee apprehends this: “For like a shaft, clear and cold, the thought pierced him that in the end the Shadow was only a small and passing thing: There was light and high beauty forever beyond its reach.”

Good triumphs, yet Tolkien’s epic does not lapse into escapism. His protagonists are nearly overwhelmed by fear and anguish, even their own lust for power. When Frodo returns to the Shire, his quest at an end, he resembles not so much the conquering hero as a shellshocked veteran. Here is a war story, wrapped in fantasy, that delivers painful truths about the human predicament.

Tolkien used the language of myth not to escape the world, but to reveal a mythic and heroic quality in the world as we find it. Perhaps this was the greatest tribute he could pay to the fallen of the Somme.

Joseph Loconte is an associate professor of history at the King’s College in New York City and the author of A Hobbit, a Wardrobe, and a Great War: How J.R.R. Tolkien and C.S. Lewis Rediscovered Faith, Friendship, and Heroism in the Cataclysm of 1914-1918.