A preliminary survey of formal concepts of "disability" from the Twelve Tables of Rome of the 5th century BCE to the Prerogativa Regis in English law of the late 13th century CE is presented. Firm conclusions are restricted by problems in translation and other limitations in available data. However, it appears that the concept of intellectual disability and its distinction from episodic mental illness first emerged in several subcultures of Western civilization during the height of ancient imperial Rome and during the early medieval period in Northern European and Arabic civilization.