For this job, they hired an experienced tractor driver. He was a hardworking and patient man, able to handle machinery even in the toughest conditions.

From early morning until late at night, his tractor roared by the river, digging trenches. Rain, wind, cold — nothing could stop him.

And then one day, just before noon, the tractor’s plow suddenly struck something hard with a loud metallic screech. The machine jolted, the engine stalled, and a rusty piece of thick chain protruded from the ground.

The tractor driver frowned. At first, he thought it was just old junk, but when he tried to pull it out, he realized the chain went deep into the earth.