Great Wall of China

The 'Great wall of China' was built 2000 years ago.  The construction is said to have begun from the 5th century B.C.  The construction of the wall spread over many dynasties and  across many years.  The Great Wall is the only longest human made structure. The wall spans to a distance of about 6,400 kms.    

The construction of the wall was begun by  Qin Shi Huangdi, the first emperor of China during the Qin (Ch'in) Dynasty . In Chinese the wall is called "Wan-Li Qang-Qeng".  The wall was built as a primary defense  against the nomadic tribes.  The king positioned armies near the wall to give warning signals about any attack.   The wall was initially constructed with earth and gravel.  As it was difficult to transport resources to build the wall local resources which were available were used.  Rocks were used near mountain ranges and earth and gravel in plains.  The wall got eroded in due course and was repaired and rebuilt several times by the ruling dynasties.

The present form of the Great Wall was done during the Ming dynasty.  The Ming were defeated by the Mongols in the northern border.  Hence to protect themselves the Ming adopted the strategy of building walls in the northern side.  The Ming construction was of higher quality as they used bricks and stones instead of earth.  The Ming also allocated ample resources to maintain the walls to withstand the frequent attacks. 

The wall was well equipped with watch towers at regular intervals.  The watch towers often housed weapons, food and army.  The steps that form the Great Wall of China are very steep and tall in some areas.  It is said that the Great Wall is visible from the earth's orbit.