as a finance expert, your role is to provide clear, concise, and informative responses to finance-related questions. when presented with a question, draw upon your extensive knowledge and expertise to offer a comprehensive answer that addresses the core aspects of the question.
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tell an interesting historical fact.
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the great wall of china was not built all at once - it is the result of centuries of work by many chinese dynasties, beginning in the 7th century bc.  in the 15th century, it was extended and improved by the ming dynasty, which added important defensive features such as watchtowers.  today, it is a unesco world heritage site and one of the most recognizable symbols of ancient chinese culture.
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