In a violent clash between rival gangs from Asnières and Gennevilliers in the banlieue north of Paris, a 15-year-old boy was killed at the metro station Les Courtilles, the last stop on Line 13. Inevitably, revenge attacks occurred. Security was heightened with hundreds of police patrolling the area, but residents and city officials alike understood that increased police presence alone would never be a long-term solution. Realising the need for radically different approaches to halt an escalation of violence, city officials, asked Sarah Harper, Artistic Director of Friches Théâtre Urbain, a street theatre company in Paris, to develop a community-based art-making project that would augment attempts by the youth workers and others to defuse the volatile situation. In "Lieu Commun," the multi-faceted project lasting 20 months, Harper developed innovative approaches to collaborative art-making resulting in vibrant public art that repeatedly interrupted the legacy of hatred between Asnières and Gennevilliers. The slow process of collaborative art-making began with symbolic links between the residents of the two towns rather than face-to-face contact, an innovative approach that eased the way for more profound activist cooperation. The co-created public art took the form of elaborate, often mobile, performance installations that began to replace the narrative of conflict that had become customary for Asnières and Gennevilliers with an opposing narrative of cooperation, both depicted in the art product and practiced in the art-making. Community collaboration in the creation of this ephemeral public art played a significant role not only in changing the character of the confrontational and often dangerous public space of the metro station, but also in altering attitudes of both residents and city officials toward the potential for art to foster cooperation and active citizenship.