Conventional wisdom holds that a select group of World War I poets and writers, Siegfried Sassoon and Wilfred Owen among them, forever changed the way we see war. In The Great War and Modern Memory (1976) historian and literary critic Paul Fussell argued that these groundbreaking writers transformed our perception of warfare from a heroic enterprise for brave soldiers to a disillusioning spectacle of waste in which youth are butchered by new and terrible technologies of death. Owen, a young officer who was killed in action just days before the war ended, most clearly conveyed this shift. His most famous poem, “Dulce et Decorum Est,” proclaims Horace’s Latin aphorism “It is sweet and fitting to die for one’s country” to be a dangerous lie. The poem can be read as an exhortation to teachers and preachers to stop telling that lie.

Another young writer, an expatriate American living in Paris, had witnessed the nightmare of trench warfare while driving a Red Cross ambulance. In Ernest Hemingway’s stories and novels—“Soldier’s Home” and A Farewell to Arms come especially to mind—we meet veterans who can no longer pray to a personal God and for whom fine words like “valor” and “honor” have stopped making sense. Hemingway’s works entered the canon not only because their minimalist narrative style revolutionized modern literature but because they dared to say that the abstract verities for which the war had been fought were rubbish.

Allen J. Frantzen directly challenges Fussell’s perspective, or at least offers a strong corrective to it. Through a careful reading of materials that include art, letters, postcards, recruitment posters and battlefield memorials, Frantzen shows that chivalry—that centuries-old medieval code of heroic sacrifice embedded in the European tradition—was not dispatched by the Great War’s modernist voices, but has remained the dominant interpretive framework for understanding wartime experience and behavior.

Though machine guns, tanks and poison gas did away with medieval ways of fighting, they did not dislodge medieval ways of thinking. Frantzen insists on the staying power of these old codes: “Chivalry reinforces group identity as it models heroic masculinity. Whether we are excited or disturbed by these avatars, we need to understand the medieval ideas, the moral and theological meanings beneath them, for these ideas, old though they are, help to explain violence in the modern world.”

Frantzen defines chivalry as a code of heroic masculinity married to a theology of Christian sacrifice. The code found its first real impetus in the court of King Arthur, and became integral to the behavior of knights during such conflicts as the Crusades and the Hundred Years War. The knight who interprets the death of Christ as a model of martyrdom that inspires him to risk his own life on behalf of others paradoxically becomes the warrior who martyrs others as well. This “sacrificial” mode of chivalry has been the core value for soldiers during the past two millennia. And, as most Memorial Day sermons suggest, it will probably continue to inspire them.

But Frantzen’s argument is more complicated, for he sees another strand of thinking in the chivalric system—a kind of minority report that he calls “antisacrificial.” In this less familiar tradition, the knight renounces violence and the heroic code, forgives his enemies, and receives the blessing of Christ.

To illustrate this road less traveled, Frantzen calls attention to a painting by the pre-Raphaelite artist Edward urne-Jones, The Miracle of the Merciful Knight (1863). The pictured knight has removed his helmet and kneels before a figure of the crucified Christ. Christ leans forward to touch his shoulders and give him a blessing. Burne-Jones’s inscription reads: “Of a Knight who forgave his enemy when he might have destroyed him and how the image of Christ kissed him in token that his acts had pleased God.”

Frantzen sees such an interrogation of the Victorian cult of “muscular Christianity” as having roots going much further back. His scholarly excursions into obscure textual thickets sometimes can be highly illuminating. For instance, Frantzen illustrates how medieval thinkers and artists recorded their ambivalence about violent knightly behavior:

A late fifteenth-century manuscript incongruously known as The Medieval Housebook contains a drawing that shows what happened when knights went to war. Under the sign of Mars, knights attack a village; one beats a peasant on the head, another strikes a farmer’s wife, and others set fire to a house. This was not how knights and their followers were supposed to behave, as we know from Ramon Llull’s Libre del orde de cavalleria, which instructs knights to use their castles and horses to protect people and specifically prohibits burning houses, stealing, and preying on the powerless—the very acts The Medieval Housebook illustrates.

Frantzen delves into World War I artifacts—recruitment posters, mass-produced postcards, war memorials—with zeal and insight. Art historians will be pleased by his attention to visual history, for the book makes clear how medieval and chivalric iconography remained overwhelmingly dominant in interpreting the war to its own participants and to posterity. The book’s lavish color plates establish the link between the Great War’s doughboys and the medieval knights of old.

Most significant is Frantzen’s assertion that “most histories fail to analyze the theological assumptions of chivalry, even as they correctly place prowess at the center of the knight’s world.” Bloody Good urges readers to think more theologically about how a peculiar interpretation of the cross came to undergird the actions of Christian knights and modern European warriors alike. We still don’t fully understand the uncanny power of this theology of sacrifice. And to consign the ancient codes of chivalry and knightly behavior to the dustbin of history—or to the geeky dungeons-and-dragons kingdoms of adolescence—is to be in denial.

The realization that we are still very much in the grip of medieval codes of thinking that define bravery, heroism and the value of sacrificing our lives and the lives of others may force us to look at those burnished museum suits of armor with new respect and fear. Figuratively and theologically, we are still bound by what that armor represents.