It took a climber’s eye to turn carabiners from a military tool into revolutionary gear. As early as the 1850s, German firefighters used carabiners for anchoring purposes, but various soldiers had already been using the metal clips to hold up their guns for decades.
In 1909 Otto “Rambo” Herzog saw firefighters practicing rescue with carabiners, and he immediately saw their potential for climbing applications. Up to that point, climbers had to untie their ropes and re-thread them through protection or use a second piece of cord to tie their protection and rope together. This often required two hands, and limited the difficulty of climbs that could be safely completed. Using carabiners, Herzog was able to establish routes—now graded as hard as 5.10.