The ancient cannons are exhibited at the Shanhaiguan Great Wall Museum in Qinhuangdao of north China's Hebei Province, July 20, 2009. The Shanhaiguan Great Wall Museum opened to public for free on Wednesday after the reconstruction which costed over 40 million yuan (about 5.8 million U.S. dollars). The museum, regarded as the "Great Wall encyclopedia", elaborates the Great Wall about its history, construction and culture by presenting the cultural relics, sculptures, pictures and models. [Li Yong/Xinhua]