Early on the morning of Nov. 12, 1958, George Whitmore, Warren Harding and Wayne Merry accomplished something many climbers considered unthinkable: They reached the top of El Capitan.

Conquering El Capitan, a 2,900-foot-tall sheer granite wall that looms over Yosemite National Park in California, seemed practically impossible given the limited tools and techniques available to alpinists of the day. The effort took the climbers 45 days, spread out over about a year and a half.

“The type of climbing had not been done before,” Whitmore said in an interview for Merry’s obituary in 2019. “We had to improvise as we went.”

In the decades since, El Cap has become one of the most famous climbs in the world. Some professional climbersascend it without ropes, or climb so rapidly they seem to sprint up the side; the speed record on a route called the Nose, set in 2018 by Tommy Caldwell and Alex Honnold, is just under two hours.