In 'Civilization and its discontents' (1930), Freud discusses the ways in which the child moves along the path of its development. The child is learning to distinguish between an internal and an external world, through its body and its perceptions. Indeed, the infant is becoming a subject through the projection of sensations onto the surface of the body, through its embodied knowledge of the realities of the world outside. At a certain point, Freud begins to discuss memory-traces in the mind. He is searching for a metaphor for the indestructibility of psychic reality. Freud selects the example of 'the history of the Eternal City' (page 256): Rome. He then traces out the founding of Rome, its domination by the Caesars, and its transformation in the Renaissance. Beneath the soil of the contemporary city can be found the memory-traces of ancient Rome, but this history is also preserved on the surface. The Eternal City is like the Eternal Mind. Temples, walls, piazzas are built and torn down as Caesars rise and fall. The history of the child's experiences is never eradicated, it is to be found in the archaeology of the city of the mind, in the dynamics of the present and in its ruins. Then Freud gives up: 'There is clearly no point in spinning our phantasy any further, for it leads to things that are unimaginable and even absurd. If we want to represent historical sequence in spatial terms we can only do it by juxtaposition in space: the same space cannot have two different contents' (1930:258).