The Great Wall of China is mostly Ming-dynasty, not ancient

The Great Wall is often dated to Emperor Qin Shi Huang (221 BC), but most of the structure tourists visit today was built during the Ming dynasty (1368–1644). Earlier walls were made of rammed earth and have largely eroded. The Ming rebuilt and extended the wall using brick and stone, adding watchtowers and beacon towers. At its longest, the Ming Great Wall stretched over 8,800 kilometres. It was also not visible from space with the naked eye — an enduring myth debunked when Chinese astronaut Yang Liwei reported seeing nothing of the sort in 2003.

Source: Waldron, The Great Wall of China (1990)