long defensive wall; long fortification wall
Refers to any long wall built for defense, such as ancient Chinese walls or similar fortifications. Not an everyday word; mostly used in historical or geographical contexts.
In China, many long defensive walls were built besides the Great Wall.
Great Wall of China
Almost always used in the full phrase 万里の長城. When 長城 appears alone in context, it usually refers to the Great Wall.
See also: 万里の長城
The Great Wall of China is registered as a World Heritage site.