The temple of heaven (above) in Beijing, the circle means heaven and the whole thing is surrounded by a square wall which represents earth,apparently,

One of the enterances to the forbidden city, in times past the only reason you would see this is if you were a eunuch, an emperors wife or were to be executed, thankfully times have changed and i made it out in one piece

Heres a couple of shots of the wall at Simatai about 100kms from beijing