Killer engines

Mortal Engines by Philip Reeve... In the distant future, the story revolves around the struggle of cities that survived a brutal war called the "Sixty Minute War." These cities remain on the desolate wasteland by using giant wheels to move around, attacking and preying on smaller cities in an effort to replenish their resources and survive. A young girl named Hester Shaw seeks revenge on the killer of her parents, who hails from London, the great mobile city. Fate throws a young man named Tom Natsworthy into her path, and together they fall from the city to the wasteland. The exciting events take them between the mobile and stationary cities, and they experience many adventures along the way.