The question of big cities has become a great issue of social debates in European countries : deep territorial rearrangements thus economic and social changes have brought about transformation of the urban space which have had consequences on social relationships and on the sense of ownership of cities by their inhabitants.Especially in lower class boroughs which are constantly undergoing reorganisations. New cultural and artistic dynamics arise and may touch the right of the populations to literally appropriate themselves the city.The project "Alter cities" is developing itself in 4 cities : Paris, Rome, Istanbul and Berlin.It aims at creating, with the support of multi-sector partnerships a 2 years experimental "Ruches Urbaines".These movable cultural centres will offer, conferences, debates and also urban walks.Cultural operators and citizens from the 4 countries will consult urban transformations made from the history of the neighbourhood.The end purpose is for the population to take part in the creation process of tomorrow's cities which they'll fill with life and not only watch as witness.