Since the board game Settlers of Catan was first released in 1995 it has sold more than 25 million copies. It works like this. Play starts after tiles of different land types – mountains producing iron ore, pastures sustaining sheep, and so on – are laid out – and numbers between 2 and 12 are randomly assigned to each tile. Every player picks a spot on the board to establish his or her first village. When the dice is rolled, a player receives a resource that matches the number on the dice if his or her village is located next to that resource. So, if the pasture next to my village has 9 on it, and the two dice thrown add up to 9, I receive one sheep. Those resources I then use to buy roads and villages and cities – and so expand my empire.