Dikes and irrigation in Ningxia trace to the beginning of dynastic rule , when the Qin rulers who unified China in 221 B.C. built irrigation for soldiers garrisoned on some of the earliest sections of the Great Wall .
Ningxia
China
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China
Ningxia
/location/location/contains
China
Ningxia
/location/country/administrative_divisions
LOCATION
Ningxia
LOCATION
China