The Great Wall of China
The Great
Wall of China is the largest defense fortification and the greatest building enterprise
ever undertaken by man. About 1500 miles long, this unique wall stretches from
the Gulf of Chihil of the Yellow see along
the northern frontier of China to Kansu province in the west. The width of this
wall varies from 15to 40 feet at the base, and from 12 to 35 feet at the
summit. Its height ranges from 20, to 500 feet. It is the only structure on
earth that can be identified from the moon. 
Walled
frontiers between the kingdoms in China date from at least the 4th
century, B. C. In the 3rd century B. C., the first emperor of “Chin”,
after uniting China, linked up the existing walls and built new sections to create
the Great continuous unit. His purpose was to defend China from Huns on the north.
Watch the towers garrison stations were set at regular intervals in order to
send signals and guard the bulwark. 
The wall was
constructed in such a way that troops summoned by beacon fire could be quickly transported
along its top. The Wall was built mostly of rubble, although the western sections
are of tamped earth and important passes are of brick or masonry. The wall was
frequently modified in later centuries. Some of its sections were built in the
15th and 16th centuries with new facilities of high
towers. “Before that extensive repairs and extensions were made at various
periods, notable during the Ming dynasty.