The correct answers are A) world’s longest human-made structure at more than four thousand miles, B) actually constructed from a series of smaller walls that were connected together, and D) built to guard against Mongol invaders.
Three characteristics of the Great Wall of China are "world’s longest human-made structure at more than four thousand miles, actually constructed from a series of smaller walls that were connected together, and built to guard against Mongol invaders."
The Great Wall of China is one of the most famous places on planet Earth and can be seen from space. It took many tears to built and join the series of walls that formed the total Great Wall. It was built to protect the territory from enemies. Construction started in early 7th century BC. Historians consider that the final construction or additions to the wall were made between 1368-1644.
UNESCO named the Great Wall of China World Heritage Site in 1987.
