By Lorris Chevalier

Among England’s many lost or disputed manuscripts, few have intrigued historians as much as the phantom book mentioned by Geoffrey of Monmouth. Allegedly the foundation for his Historia Regum Britanniae, this mysterious text played a key role in shaping the myths that legitimised the Norman kings—especially Henry II. Yet, no copy of the book has ever been found, leaving scholars to question whether it was a genuine source or a clever literary invention.

A Book Without a Name

Geoffrey of Monmouth refers to this book in the introduction to his Historia Regum Britanniae. He claims to have received it from Walter, Archdeacon of Oxford, who supposedly presented it as an unquestionably authentic text recounting the history of Britain’s kings from Brutus of Troy onwards. Written in the Breton language, this manuscript supposedly chronicled the great deeds of legendary rulers and served as the foundation for Geoffrey’s work.

However, this book has never been found. No contemporary chroniclers mention it, and no manuscript seems to match its description. Its absence has fuelled historians’ doubts: was the book a deliberate fabrication to lend credibility to Geoffrey’s account, or was it a real text that has since been lost?

A Tool of Political Legitimisation

The significance of this phantom book is less about its physical existence and more about its symbolic power. By tracing British history to a prestigious past and linking the royal lineage to semimythical figures such as Arthur or Brutus of Troy, this phantom book gave the Plantagenets a powerful tool to legitimise their rule.

Henry II, who ascended the throne in 1154, came from a still-young dynasty. His mother, Empress Matilda, had fought to assert her rights against Stephen of Blois, and the Plantagenets’ legitimacy was far from unassailable. The revival of the Arthurian myth and the use of a glorious past as political validation were thus strategic moves. Indeed, under his reign, there was a renewed interest in legendary figures: Arthur became a state hero, and the English dynasty was firmly embedded within the continuity of Britain’s mythical kings.

A Historical Fable?

If this book truly existed, it was likely a composite collection, blending oral traditions with mythologised history. But its absence from archives and the fact that only Geoffrey mentions it sustain the hypothesis of a purely literary creation.

The debate divides scholars between those who seek the historical Arthur and those who study the “Arthurian matter”—its sources, functions, and impact.: its sources, functions, and impacts. In both cases, it is evident that Geoffrey of Monmouth’s influence was decisive. Did Geoffrey invent everything? Was he proficient enough in Welsh to translate such a complex book? Did he have access to a document unknown to all other clerics involved in writing Britain’s history?

These seemingly simple questions reveal the complexity of studying medieval sources. While our modern approach to truth relies on evidence, the study of the History of the Kings of Britain demonstrates that the expectations of a 12th-century audience were quite different.

By filling a void he considered “remarkable” with his mysterious source, Geoffrey employed several well-documented methods. First, invoking an established authority was a common practice among chroniclers and historians of his time. Though he names some of these figures, he nonetheless manipulates their content in favour of “his” history of Britain. What matters here is not so much fidelity to an inaccessible original document, but rather the act of seeking validation from other sources for the present. Early Arthurian scholars harshly criticised this as a betrayal, whereas others have praised it as an effective and inspired construction with exemplary coherence.

Whether it existed or not, this phantom book fulfilled its purpose: it gave rise to one of the most influential chronicles of the Middle Ages and served as a cornerstone for the legitimisation of English kings. A book that “made kings,” not through its substance, but through its evocative power.

A Fusion of Traditions

The reference to a mysterious book thus provides Geoffrey with a link between two different conceptions of knowledge—conceptions that, while not in direct conflict, reflect a profound paradigm shift. Oral traditions, once considered the foundation of a society’s identity, were losing their value amid the explosion of written records. The book in Old Breton, a gift from Walter of Oxford, allowed Geoffrey to fill the gaps left by written sources without admitting reliance on collective knowledge. By not naming it, he avoided comparisons and criticism. It also made him appear better informed, more erudite, and superior to others who sought to write the history of a rapidly changing land.

More specifically, translating from Old Breton (Welsh) into Latin allowed Geoffrey to irrevocably link Arthur’s heirs, the Angevins, to the Trojan Brutus, the first king of Britain:

Brutus then gave his name to the island of Britain and called his companions the Britons, wishing thereby to perpetuate his memory. A little later, the language of this people, originally called the Trojan or derivative Greek language, became the Breton language.

The question of the existence of the mysterious book in the Breton language continues to inspire research; some see it as the Historia Britonum, compiled around 870 by Nennius, while others detect traces of the Annales Cambriae, or simply accuse Geoffrey of forgery. Ultimately, these fascinating investigations eloquently demonstrate that the author succeeded in his ambitious goal. Through this phantom book, he crafted a history of Britain that irrevocably tied his patron to the island’s supernatural past, providing him with a sacred ancestor—one even more extraordinary than Charlemagne—none other than Arthur, the conqueror of all Europe.

Dr Lorris Chevalier, who has a Ph.D. in medieval literature, is a historical advisor for movies, including The Last Duel and Napoleon. Click here to view his website.

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Further Readings:

Geneviève Pigeon, “Le Livre qui fait les rois,” Fabula-LhT, n° 13 (2014)

Top Image: British Library MS Royal 20 A. II, f.3v