Because the people from Mongolia went around the bridge because it was not long enough.
To keep Invaders out of China
The Monguls
To protect china from invaders!
it was used to keep out invaders
The Great Wall was constructed to help defend against invaders, like the Mongols.
to keep invaders out
the great wall
it protected them from invaders and wars!
to keep out the Mongol invaders
The great wall of China is on its border ,it was built to prevent invaders.
To stop the northern invaders.
It was built to protect China from Mongolian invaders.