Did the Great Wall of China work?


https://www.nationalgeographic.com/history/magazine/2016/03-04/the-great-wall-of-china/?cmpid=org=ngp::mc=crm-email::src=ngp::cmp=editorial::add=SpecialEdition_Escape_20201202&rid=5DAE86AE0897F2B2819B70CBE95CD107