The Great Wall of China was constructed beginning in the 3rd century BC to protect ancient Chinese states and empires from invasions by nomadic groups on the northern steppes. It was built as a series of fortifications stretching east to west made of various materials like stone, brick, and wood, forming a barrier along China's northern border.

1. CONSTRUCTION OF THE GREAT WALL OF
CHINA BEGINS
• The great wall of china is a series of fortifications made of
stone , brick, tamped, earth, wood and other meterials.
• generally built along east to west line across the historical
northern
• to protect the chinese states and empies against the raids
and invasions of the various hamadic groups of the
Eurosian steppe
Source :
http://www.travelchinaguide.com/china_grea
t_wall/facts/who-built.htm