My purpose in this paper is to sketch the main features of Heidegger's interpretation of Greek philosophy during the period of fundamental ontology. It refers to a time when Heidegger had not yet attempted to find, underneath metaphysics or beyond it, a way to a more thinking thought. This means rather a time when Heidegger, instead of being busy with the overcoming of metaphysics, explicitly claimed that his ambition was to accomplish metaphysics as the science of Being.