请帮我回答这个问题：1.How old is the Great Wall?有助于回答者给出准确的答案

中国的长城是人类文明史上最伟大的建筑工程，它始建于2000多年前的春秋战国时期，秦朝统一中国之后联成万里长城。汉、明两代又曾大规模修筑。其工程之浩繁，气势之雄伟，堪称世界奇迹。
The Great Wall of China is the history of human civilization's greatest works, which was built 2,000 years ago in the Spring and Autumn Period, the Qin Dynasty after the reunification of China into the Great Wall. Han and Ming dynasties have also been large-scale construction. Their voluminous works, the momentum of the grand, can be called a miracle in the world.

这长城有多长?

公元前221之后的一段年代是泰始皇建长城的主要年代.
但之前己有一些国家为了抵抗外侵建了一些长城,不过较简单,只能算是围墙.
所以长城至今己有2200多年了.

长城存在的年代多久了？？