Hi, the wall was built by laying bricks or stones on mountains. It was built in ten cities or provinces in northern China. It measures 4 to 5 meters tall. Today many has been ruined and many are repaired and opened as scenic sight. It took over 2,000 years to build the wall. For the detailed info, I think you may refer to Great Wall of China(https://www.travelchinaguide.com/china_great_wall/) . There are parts introducing Great Wall Sections, construction, History and so on.