I have never visited but I imagine two people one on either side cannot hear each other even if they shouted, and of course cannot see each other. The etymology need not be based on history or practical use.
replyI've lived in China and visited multiple times and you could certainly shout and hear someone from the other side (if you are not in touristy noisy section), it's really not that huge while you are right under the wall. I mean if you can shout in mountain and someone can hear you hundreds of meters away, they can certainly hear you over some 2-3 floors tall building.
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