Athens, Carthage, Rome. History shows us examples of independent cities that were their own worlds, offering freedom of ideas and a model for social cohesion, where people could live freely in an ideal republic. Cities can still drive social progress – but what are the challenges, and how can cities lead society today? CBC Ideas’ Paul Kennedy moderates a discussion featuring CivicAction CEO Sevaun Palvetzian,  8 80 Cities founder Gil Penalosa and Lorna Day, director of urban design for the City of Toronto.