Fort-makers and fort-breakers alike were playing a sort of chess-game with geometry. Light, which conveyed intelligence, moved in straight lines, and musket-balls, which killed over short distances, nearly did. Cannonballs, which broke down forts, moved in flattish parabolas, and mortars, which destroyed cities, in high ones. Fortifications were now made of dirt, which was cheap, abundant, and stopped projectiles. The dirt was mounded up and shaved into prisms—volumes bounded by intersecting planes. Each plane was an intention to control its edges. Lines of sight and flights of musket-balls were supposed to skim along these, seeing and killing whatever presented itself at the creases. It was hoped that cannonballs would come in perpendicularly and dig their own graves, as opposed to glancing off and bounding to and fro like murderous three-year-olds. Cavalry-stables, infantry-barracks, powder-houses, and gangways were etched into the dirt-piles in the places where cannonballs were least likely to reach. The human parts were utterly subordinated to the demands of geometry. It was a desert of ramps and planes.