Just as in free climbing, the usual aid technique involves two climbers, a leader and a belayer. The leader is connected by a rope to the belayer, who remains at the belay station while the leader moves up. As the leader advances, the rope is let out by the belayer, and clipped by the leader into the pieces of protection as they are placed. If the leader falls, the belayer locks off the rope and, assuming the protection doesn't pull out, catches the leader's fall on the rope. When the leader, moving up, reaches the end of the rope, or a convenient stopping point, they build an anchor, hang on it, and affix the rope to it. This then becomes the next belay station. The belayer then ascends the fixed rope using mechanical ascenders, retrieving the protection that was placed by the leader. Meanwhile, the leader sets up a hauling system and, using another rope brought up for that purpose, hauls up a bag containing the climbers' food, water, hammocks or porta-ledge, sleeping bags, and so on. Many variations on this basic technique are possible, including solo aid climbing and climbing with a team of three or more.