[Photo provided to China Daily]

"He fashioned the wires into a half circle with a long handle and then gradually put that circle through the opening, noosed the stone slab on the top and pushed," says Yang, who has lived in a retirement home in suburban Beijing since her husband died at the age of 84 in 2010.

"The upper edge of the stone slab, the part that was in contact with the gate, was slightly lifted backward, so the gate could be pushed open just a little bit," she says.

A little bit indeed, but big enough for Sun, back then a thin 18-year-old, to squeeze through.

That was in May 1957. A year had passed from when the team members had dug out their first shovel of dirt.