Solnit has a point to make: walking, in this non-dominating and absorbent way, is necessary to the life of the city. Walkers, she says, quoting the French psycho-geographer Michel de Certeau, "are ' practitioners of the city' ... the city is made to be walked, a language, a repository of possibilities, and walking is the act of speaking that language, of selecting from those possibilities". This intriguing idea has its down side. In America, the human body, once seen as a work horse, is now treated as a pet, given outings in a gym and perhaps occasionally on a hike but otherwise driven from place to place. Solnit has watched people in San Francisco-queuing in their cars waiting for a parking slot immediately outside the shop where they are going to buy their mountaineering boots. If people stop walking in their cities, as they have in America, then in some ways the meaning of the city disappears. "A post-pedestrian city," Rebecca Solnit says, "has not only fallen silent but risks becoming a dead language, one whose colloquial phrases, jokes and curses will vanish, even if its formal grammar survives." Streets need the ruissellement de paroles, the rustling stream of words to stay alive. Walking, by somehow integrating the body, the mind and the inhabited place, civilises the world.