There are numerous typologies of barriers that separate inside & outside physically, metaphysically, and intellectually. The boundary as a physical marking (whether it is the simple line Romulus drew to delineate Rome, the Greek Khôra at the boundary of the Greek Polis – or in Plato's account, the original space of all forms, an interval neither being nor nonbeing –, the Todesstreifen/Death Strip that separated East and West Germany/Berlin, or the sound barrier, the asymptote of an equilibrium, letterpress printing, the cloud, enlightenment) evokes the desire and curiosity for crossing. It imbues ‘crossing’ with new meanings, memories, and encounters.