From Rousseau to Hugo, Paris became an industrial city. This transformation took place in the midst of an industrialization that threw into question the relationship between citizens and their environment. The development of hazardous activities was a challenge for the Ancien Régime society, and this led to a transformation in law and in the representation of Paris. A complex process gave factories the possibility of establishing themselves in towns. As part of the new approach of modern manufacturing, Paris became the laboratory for testing the legitimacy of pollution, ushering in an alliance between the state, science, and industry, in an entirely new kind of political project for a new and modern capital.