Back to the future where the first emperor of dynasty Qin 秦始皇 started this mega projects to protect is country from invasion. For more details you can get through the net. But for my walk here for half a day really cannot be walked finished. Can't even see the start and end point. According to the local guide, these walls really are superb and strong even more than 300 years old until today. I can't imagine those knowledge about technology were far more superior during back then. The feeling of gigantic and sturdy upon steeping on it makes you feel magnificent and impressive. That really suits the title of seven wonders in the world.