At the dawn of the third millennium, planet Earth entered a zone of turbulence. The 2008 crisis added economic uncertainty to the threat of global warming and extreme events such as droughts, floods and cyclones, the persisting crisis of p- erty and the spectrum of pandemics and terrorism. Against this global landscape in an era of fragility, cities, already sheltering more than half of humankind, appear as Janus-faced realities, the best and worst of places, vulnerable but still full of hope a ...