June 12 marked the official 40-year anniversary of Raiders of the Lost Ark, the first film in the Indiana Jones epic adventure series starring Harrison Ford.

Ford rose to popularity after playing Han Solo in Star Wars, and director Steven Spielberg tapped him for the whip-cracking Indiana Jones role after Tom Selleck backed out. What some fans may not realize is that the actor performed many of his own stunts, including that famous boulder chase. And Spielberg once called himself an “idiot” for putting Ford in that situation. //

Spielberg explained that they had to take the proper safety precautions to prevent injuries. But filming Ford directly from the front worked best for the scene “because the rock was more effective chasing Harrison with Harrison running toward camera, it just didn’t work as well having him doubled.” //

“A double would have cheated his head down, so Harrison volunteered to do it himself,” wrote Spielberg. “He succeeded. There were five shots of the rock from five different angles — each one done separately, each one done twice — so Harrison had to race the rock ten times. He won ten times — and beat the odds. He was lucky — and I was an idiot for letting him try it.” //

Though it was only a fake prop, Spielberg revealed it could have caused real damage to anyone in its path. Like death-level damage. He said it stood 12 feet and weighed 300 pounds. //

“We went to great lengths to make a 12-foot rock out of fiberglass and wood and plaster precisely so that it wouldn’t weigh as much as a real 12-foot boulder,” Spielberg recalled. “So whether it weighed 300 pounds, which it did, or whether it weighed 80 tons, as it would have, it could still have done bodily harm to anyone falling beneath it…” //

To operate it, they used a special rod hidden among rubber stalagmites on set. The entire contraption required a fully constructed set that could accommodate all its moving parts and enable the fake boulder to move 40 yards.