Alpine rock climbing involves technical skills including the ability to place anchors into the rock to safely ascend a mountain. In some cases, climbers may have to climb multiple pitches of rock in order to reach the top. Typically, for any one pitch, there is a belayer who is stationary and creates tension on the rope to catch a climber should he or she fall, and a climber who ascends the rock. The first climber, called the "leader", will reach a point on the rock and then build an anchor, which will secure subsequent climbers. Anchors could be created by using slings around a tree or boulder, or by using protection devices like cams and nuts.