A piton is a metal spike that rock climbers hammer into cracks in a cliff face to help them climb safely. Think of it like a sturdy metal nail with a ring or hole at one end: the climber pounds the pointed end deep into a crack in the rock, then clips their rope through the ring. If they slip, the piton (and the rope attached to it) catches their fall.

Pitons were essential tools for mountaineers tackling difficult climbs throughout the 1900s. Before modern climbing equipment, reaching the summit of places like Yosemite's towering granite walls would have been nearly impossible without pitons. Climbers would carry dozens of them, placing them as they ascended and sometimes removing them on the way down.

Today, climbers often use removable devices called cams instead, since hammering pitons into the rock damages it over time. But pitons remain important for certain climbs, and you'll still see old pitons left in famous rock faces from historic ascents decades ago.