Great Wall Built By
Warring States 445–222 BC
Qin Dynasty 221–206 BC
Han Dynasty 206 BC – 220 AD
N. Wei Dynasty 385–584
N. Qi / Sui Dynasty 550
Liao / Jin Dynasty 1066–1234
Ming Dynasty 1368–1644

Total years building the wall 1,400 -
40,000 laborers each year
Some were captured enemies, some slaves and some soldiers ordered to build. China owned the land and didn't build where there were rivers. They said it was built for psychological reasons, to scare the enemy. It didn't stop anyone from crossing it. It was too long to man.

The wall was just another Trump suggestion. That's why it's difficult to find any experts say it can be built. He doen't talk about it much now that he's on the way to get elected. Bait and Switch