In an urban conditi on where fronti ers have been torn down and citi es have become never-ending, the historical and visual limits that used to defi ne urban areas are now hard to read. For example, the conventi onal borders such as the limit between city and country do not exist anymore. Only naturalphysical limits remain, for example, between land and sea. In these conditi ons, where the border is basically an abstract element, the questi on is asked about what happens when it is designed or when it is decided to work specifi cally on the border spaces and their physical limits, with their obvious identi fi cati on problems. On the basis of these ideas, the study has focused on three important citi es: Copenhagen and its fi xed link (Oresund bridge); Venice and its MOSE project; and Antwerp with its PROAP project along the quays.