I'm kinda the vibe this is a joke question, but whatevs.

The Great Wall of China was built primarily by soldiers, forced peasant labor, and convict labor. So, yes, I suppose that slave labor was used.

It was actually built to the form we recognize over a period of about 1500 (!), but not really continuously. The first wall was created by China's first and probably most infamous Emperor, Qin Shi Huang. It looked anything from a ton of roughly cut bricks stacked together into a makeshift fence or dirt compacted with straw for strength.

The "modern" wall that we know today was built by the Ming Dynasty in the 1400s; the Ming also built what we know today as the Imperial/Forbidden City of Beijing. The Ming used legitimate bricks and stone rather than just packed dirt, but much of the lesser reinforced areas were little more than the original packed dirt structure "plated" with stone and bricks on the Northern face for additional protection.