How to design the metropolis of the future? How to face urban expansion and at the same time make sure that both, cities as well as peripheries and surrounding areas – becoming increasingly interconnected – o!er an environment worth living? In this article the authors put forward a vision for the urban fringe of Berlin as a Metropolitan Ecotone between the built-up area of the city and rural Brandenburg. As an area of experimental multifunctionality and partial self-su"ciency, the Ecotone could be the new urbanity. It could enable Berlin and Brandenburg to function as a single complex realm whose systems are continually learning from and adapting to each other.