The human race has been preoccupied with cities since before the Roman Empire. We've built, destroyed and rebuilt many thousands of complex metropolises. Now more of us live in the midst of the urban sprawl than among the landscapes of the natural world, and cities have become a daily reality for most. In many ways this is no great surprise. Cities offer us much that is unavailable elsewhere: health care, housing, job opportunities and public transport, for example. Yet these many conveniences are matched by problems. In no environment is this more apparent than the megacities of the world. These global hubs with populations exceeding 10 million demonstrate the best and worst of humanity. In them we see affluence, innovation and high standards of living, but also terrible poverty, crime and issues of mental health. Weapons of Reason's second issue seeks to better understand megacities - to find out what has made them this way and how they might develop in future. We've spoken to those who know best: academics on the front line of pioneering research, reporters who are specialists in their field, and most importantly of all, the people who live in megacities across the world.