aid climbing and climbing with a team of three or more. Until the 1940s protection was provided by the piton, driven into a crack in the rock with a hammer and stoppers. Today, aid climbing uses a considerably larger array of hardware than the pitons used by the first climbers although the primary technique of ascension has not much evolved. The typical gear of an aid climber includes pitons, hooks, copperheads, nuts, camming devices, ascenders, hauling pulleys, aiders, daisy chains, and wall hammers. The invention of camming devices or "friends" and other non-damaging rock gear has resulted in the practice of clean aid, where nothing is hammered, a great bonus for popular routes which could be disfigured from continual hammering. The hardest aid routes are poorly protected, requiring the climber to make long sequences of moves using hooks or tenuous placements. On these routes, a climber may have to commit to moving up onto the most marginal of placements risking long and sometimes dangerous falls. By contrast, the vast majority of aid ascents are done on popular free climbs which are too difficult for the aid party to free, but offer excellent gear placements. Since aid climbing is extremely slow compared to free climbing, this can lead to some conflicts between aid climbers and free climbers waiting to climb a route. There is additional tension caused by the damage that aid climbing often does to routes. Hooks frequently break or otherwise damage holds that human hands and feet do not. New aid climbers also often compulsively "bounce test" pieces the reliability of which experienced leaders can often assess at a glance; removing a "bounce-tested" nut often requires hammer blows which further expand and sometimes fracture holds. History Until the 1960s or so, aid climbing was normal practice in most climbing areas. But as improvements in technique and equipment meant that many aid routes could be climbed free, some influential climbers began to criticise the use of aid as being against the spirit of mountaineering. Reinhold Messner wrote, "Rock faces are no longer overcome by climbing skill, but are humbled, pitch by pitch, by methodical manual labour ... Who has polluted the pure spring of mountaineering?" (from "The Murder of the Impossible"). Free climbing is now the mainstream of climbing. But aid climbers have answered the criticism of Messner and others by climbing routes where the absence of holds or features