Ancient China’s main rivers ran west to east ... which were constantly battling nomadic tribes. So the emperor’s officials press-ganged an estimated million workers, mostly farmers, into ...

The Great Wall was built to secure ancient China ’s northern borders against nomadic groups from the Eurasian Steppe.

It also sheds light on the origin and migration patterns of a nomadic empire that once ruled parts of northeastern Asia. Emperor Wu was a ruler of the Northern Zhou dynasty in ancient China.