Constant did not join SI at that time. He objected to the SI on the ground that the movement seemed to be established mainly by artists who have their own interest at heart more than a common goal. When SI openly pleaded for 'unitary urbanism', as defined by Constant and Debord, Constant joined. An intensive correspondence between him and Debord followed. Constant wrote several theoretical articles for the French SI journal and staged events at several museums in Paris as well as the Stedelijk Museum in Amsterdam, where he showed his "New Babylon" series in 1959.