Developments internal to the study of history have played a significant if overlooked role in the changing status of history within political economy. This article illustrates that claim by way of a survey of the place of history in the writings of Adam Smith, Karl Marx, and Alfred Marshall. It identifies a sea change in historical thought after the French Revolution, such that Smith's basic contrast of modern with ancient society was replaced in the thought of both Marx and Marshall by a contrast between the modern and the traditional, where the latter consisted of agrarian societies of one sort or another, distinguished according to their particular form of social bond and land ownership. But the discovery of human prehistory in the second half of the nineteenth century undermined the historical presuppositions shared by Marx and Marshall, leading both to revise not only their earlier historical accounts but also their conceptions of the relationship between the historical and the economic. While the discovery of prehistory can be seen as returning Smith's ``primitives'' to the historiographical stage, it also played an important part in fostering the twentieth-century separation of economics from history.