The Great Wall of China was built to protect China from the marauding tribes to the north. Construction began in the 7th Century BC and the most well-known section was built in the Ming Dynasty (1368 – 1644).
Watch towers and garrison stations were built at strategic placements for protection from enemys. The wall was also used to transport of goods and to control immigration and migration. Archaelogical surveys determine that the wall measures over 21,000 kms.