The Great Wall of China is 21, 196 km long
Clearing the land to raise crops because
During the process to clear the land, humans began to understand how to deal with plants, and which species are better adapted to that kind of land
It would definitely be a long, expensive process. Before the Gutenberg press, anything that was to be printed would have to be hand-copied, whether it was a 2-page pamphlet or a 200-page book!