Barcelona is a densely populated city situated on a small plain between the sea and the Collserola mountain range. An old town with the Rambla as its main axis. The outlying towns annexed by the city in the 19th century-Sant Marti, Gracia, Sarria, Sants-are now neighborhoods with a character of their own. The Eixample (enlargement) designed by Cerda serves as a dynamic mesh that allows for many different uses. The housing developments that grew up as a periphery in the 1960s and 1970s have today been integrated into the city. The ring roads with their heavy traffic surrounded and defined the city in the 1990s. The city-territory that we can now see owes its existence to the co-operation of surrounding towns-Badalona and Hospitalet, but also Mataro, Terrassa and Vilafranca del Penedes. Barcelona is a territory, an artificial environment, an accumulation of history, a corner in the Mediterranean, which can only grow by means of a network that is articulated with the collaboration of other cities, from Lisbon to Rome, from Seville to Brussels.