In Philip Reeves' Mortal Engines and Predator's Gold, Traction Cities are vast metropolises built on tiers that move on gigantic caterpillar tracks. These cities hunt smaller cities which in turn hunt towns which in turn also hunt static settlements in a practice known as Municipal Darwinism. Traction cities included London, Paris, Arkangel , Anchorage and Marsailles. These municipalities were formed after the Sixty Minute War which resulted in the deaths of millions, a barren earth and the loss of most technological knowledge. After the war, many people and their municipalities were mobilised into vast tiers that move on caterpillar tracks. Their worst enemy is the Anti-Traction League which opposes Municipal Darwinism and Traction cities.