Chinese cities were defined from the Shang and Zhou periods by massive walls built of rammed earth (hangtu), in which moist earth was compacted layer by layer between timber shuttering. Later walls were faced in brick, but the rammed-earth core endured, and the very word for city, cheng, also means "wall". Walls enclosed not merely a settlement but a hierarchically administered unit, with gates, watchtowers and a moat. Capitals such as Ming Beijing carried inner and outer wall circuits many kilometres long.
The wall was the constitutive technology of the Chinese city, fixing its outline, defence and administrative identity for some three millennia.
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