UIAA uses both style and ethics in its argument, but the goal is to protect some areas that may be the arena for what they call "adventure climbing". Types of climbing Most of the climbing done in modern times is considered free climbing—climbing using one's own physical strength, with equipment used solely as protection and not as support—as opposed to aid climbing, the gear-dependent form of climbing that was dominant in the sport's earlier days. Free climbing is typically divided into several styles that differ from one another depending on the choice of equipment used and the configurations of their belay, rope and anchor systems. As routes get higher off the ground, the increased risk of life-threatening injuries necessitates additional safety measures. A variety of specialized climbing techniques and climbing equipment exists to provide that safety. Climbers will usually work in pairs and utilize a system of ropes and anchors designed to catch falls. Ropes and anchors can be configured in different ways to suit many styles of climbing, and roped climbing are thus divided into further sub-types that vary based on how their belay systems are set up. Generally speaking, beginners will start with top roping and/or easy bouldering and work their way up to lead climbing and beyond. Due to the length of time and extended endurance required, and because accidents are most likely to happen on the descent, rock climbers do not usually climb back down the route, or "downclimb," especially on the larger multiple pitch class III–IV, or multi-day grade IV–VI climbs. Aid Still the most popular method of climbing big walls, aid climbers make progress up a wall by repeatedly placing and weighting gear that is used directly to aid ascent and enhance safety. This form of climbing is typically used when ascent is too technically difficult or impossible for free climbing. Free The most commonly used method to ascend climbs refers to climbs where the climber's own physical strength and skill are relied upon to accomplish the climb. Free climbing may rely on top rope belay systems, or on lead climbing to establish protection and the belay stations. Anchors, ropes and protection are used to back up the climber and are passive as opposed to active ascending aids. Sub-types of free climbing are trad climbing and sport climbing. Free climbing is generally done as "clean lead" meaning no pitons or pins are used as