Nanjing, China City Walls

The largest city wall in the world is in Nanjing, China. It was built between 1366 and 1386 by the Ming Dynasty Emperor Zhu Yuangzhang to enclose and fortify his capital city. The wall is over 33 km long, is constructed from 350 million bricks, and is 14 meters wide, and 14-20 meters high. Its 13 massive gates today have been restored and house museums telling the story of the city of Nanjing. The ASTER image was acquired October 25, 2014, covers an area of 20.5 by 21.6 kilometers, and is located at 32.1 degrees north and 118.7 degrees east.

https://photojournal.jpl.nasa.gov/catalog/PIA22735