The main aim of this paper is to bring to the surface and clarify some basic ideas on which Karl Marx’s philosophy of history rests. Although the materialist conception of history is a theme already widely discussed in Marxist literature, the specificity of our study lies in the perspective adopted, which is the one proper to the history of ideas. More precisely, we provide support for the thesis that Marx does not just observe "empirical facts" and discover "natural laws of history", as repeatedly claimed, but rather, he organizes a large body of historical data on the basis of certain "ideas" that are no less speculative and controversial than those produced by Old and Young Hegelians. This does not mean, however, that these ideas are necessarily devoid of cognitive power.