The Great Wall of China was one of the greatest public
works ever built by an empire in the entire world. It was built by the
Chinese to keep the Xiang Nu, or mongolians, from attacking the Chinese
that lived on the Mongolia. The wall built by the Han Dynasty was just
an extension of the Qin great wall. The wall was extended all the way to
Xin Jiang in the west. Beacon towers were erected along the wall to warn
the other towers of attack. Ancient records report that at least one
million slaves and prisoners of war were used to create this defensive wall.
Many laborers died from exhaustion and starvation while working on this colossal
task, their bodies added to the rubble and masonry as the quickest means
of disposal. For centuries, the Wall was known as "the longest cemetery in
the world." Along with the construction of the Great Wall, laborers had to
build small canals and reservoirs. All peasants who were farmers were required
to harvest their grain and put it in granaries/
(http://hyperion.advanced.org/18778/great.htm)
http://www.bergen.org/AAST/Projects/ChinaHistory/CHIN.HTM