"A Regnal Genealogy in Trouble" contends that the Trojan myth served as a cultural locus for medieval English writers to explore the infamous heritage that came from the traumatic Trojan past when they contemplated contemporaneous social, political, and religious issues through the Trojan traumas. The Trojan genealogy locates the beginning of British national historiography in Aeneas' great-grandson, Brutus, who liberated his Trojan compatriots from slavery under the Greeks and subsequently founded Britain. As medieval England experienced social turbulence such as the Norman Conquest and the Hundred Years War, the Trojan myth reverberated in dynastic chronicles, alliterative or historical romances and even saints' lives. While the Trojan legend can be fantasized as an imperial and national claim, this project draws on the theories of trauma studies to analyze how the story of Troy functions or malfunctions as the basis of a regnal genealogy and a national historiography. Examining the Trojan origin in Geoffrey of Monmouth's twelfth-century Historia regum Britanniae , this study scrutinizes how the Trojan incident served as the founding trauma in the Galfridian historiography for different ethnic groups—the Britons, Anglo-Normans, and Anglo-Saxons—in the twelfth and thirteenth century. Fourteenth-century English writers such as the poets of Sir Gawain and the Green Knight and St. Erkenwald also revisited this literary tradition from the perspectives of the cultural conflicts between the central and regional courts, and of the traumatic impacts that the religious conversion had brought. This project culminates in examining how European and English Trojan traditions converged in Geoffrey Chaucer's works when the story of Troy was reconsidered as a traumatic national historiography in the end of the fourteenth century.