Challenging the standard view that England emerged as a dominant power and Wales faded into obscurity after Edward I's conquest in 1282, this book considers how Welsh (and British) history became an enduringly potent instrument of political power in the late Middle Ages. Brought into the broader stream of political consciousness by major baronial families from the March (the borderlands between England and Wales), this inventive history generated a new brand of literature interested in succession, land rights, and the origins of imperial power, as imagined by Geoffrey of Monmouth. These marcher families leveraged their ancestral, political, and ideological ties to Wales in order to strengthen their political power, both regionally and nationally, through the patronage of historical and genealogical texts that reimagined the Welsh past on their terms. In doing so, they brought ideas of Welsh history to a wider audience than previously recognized and came to have a profound effect on late medieval thought about empire, monarchy, and succession.