There is a pseudoscientific theory popularized by Russian authors Fomenko and Nosovsky which, among other things, claims that the Great Wall of China had been built by peoples living to the north of it who were more advanced than the Chinese at the time, and, therefore, its goal was to protect the North from the Southern barbarians (the Chinese), not the other way around.
As a proof of that claim they mention that the loopholes on the Great Wall face the Chinese side.
I don't in any way support that theory but is that very fact (loopholes facing the Chinese side) true? And if yes, as a side question, why is it so?