Many interpreters of the Historia regum Britannie have seen in its invention of a glorious British royal past a work of ethnic or national partisanship, a brief for Welsh (or Breton or Cornish) collective pride. This is a reasonable account, and remains dominant in discussions of Geoffrey's Historia. And yet there are moments in which the narrative's inflections of gens identity quite exceed simple ethnic partisanship. Pure, bounded ethnic or national essences are not entirely what the Historia is about. Via postcolonial and cultural studies, scholars have uncovered a certain ambivalence in the text's deployment of collective identities.Of particular interest are textual phenomena that threaten the idea of the ancient British gens as a unitary, bounded identity: conmixtio, that is, intermarriage, though the word is also used for the confusion of a battlefield; exterminatio, the spectre of a people's elimination and yet something that is never actually accomplished; and masquerading as another, usually someone of another gens. The latter forms the subject of this article. In what follows I hope to demonstrate some ways in which the Historia's frequent masquerades, episodes of performing as the other, respond to a continuing flux in what it meant to be English in England of the 1130s, when Geoffrey first penned his text.

The Historia enacts many scenes of masquerade; the highlights may be summarized briefly. Dunwallo Molmutius, an ambitious aspirant to the British throne in the pre-Roman period, dons enemy armor to defeat his rivals. Considered cowardly in a similar scene, the ruse is not censured in Dunwallo's case. In the period of the Roman Empire, Claudius Caesar's general, Lelius Hamo, passes as a British noble in the midst of a battle – an act that gives him access to the British king, whom he quietly assassinates. He then slips away from his ‘unspeakable victory’ (nefanda uictoria) to resume his role on the Roman side. His triumph proves empty, for the fallen king's brother, Arvirargus, surreptitiously assumes the royal armor and role. Unaware of the real king's death, the British army under the assumed king's command defeats the Romans, and Lelius is cut down in his attempted flight. Arvirargus remains king thereafter.