Why was the Great Wall of China built?

It was built to keep the rabbits out.

It was build to protect the north boarder of China from attack. Due to its long history it was not just build to protect China from the Mongols but any invader that came from the north.

China emperors weak. We have weak army, that cannot protect from Mongols. Emperor order wall to be build, to protect northern border. =))

To Keep The Mongols from invading China it was set up to be an ultimate defense against them.

they feared mongol invasion... thought wall will protect them... but kublai khan proved them wrong... :P

to protect people against foreigner like mongols and even russian (don't know what they called by that time)

To keep the mongols out.

to keep out foriegn invaders! those flippin crazy barbarians like conan. oh wait, he's fictional.... to keep out the nomadic mongols like Genghis himself

It was built to keep out intruders... I think the Mongols specifically