  So, why does Heidegger give such pride of place to Meyer’s poem? The answer to this puzzle (which too few readers even notice) is that the poem introduces the broader philosophical context of Heidegger’s project by conveying his emerging understanding of historicity, the doctrine according to which our fundamental sense of reality changes over  time.[34] The ontological “truth” that Meyer’s poem embodies—and “sets to work,” in Heidegger’s creative appropriation of the poem—is that truth itself is essentially historical and, moreover, that this essential history of truth forms three successive “epochs,” in the same way that the “jet” of water fills the three consecutive “basins” in Meyer’s eponymous  fountain.[35] For Heidegger, to put it more precisely, the relations Meyer’s poem describes between the fountain’s original “jet” and its three successive water basins illuminate the relations between “being” itself (that is, as we will see, the inexhaustible ontological source of historical intelligibility) and the three main historical “epochs” or ages in Western humanity’s understanding of being (as Heidegger conceived of this “history of being” in 1936), namely, ancient “Greece,” “the middle ages,” and “the modern age” (PLT 76–7/GA5  64–5).[36]