After accomplishing the modest feat of founding the Ming Dynasty more than 600 years ago, Emperor Zhu Yuanzhang was apparently still unsatisfied with his achievements and commissioned a grandiose wall to protect China's new capital city of Nanjing. The ambitious defense project called for granite foundations and intricate layers of boulders and limestone. A special concoction of lime, tung oil and glutinous rice secured the layers together. Because of the meticulous building process, most of the ancient city wall still stands. Of the 33.5 km original wall, more than 20 km still encircles the ancient city bearing true testament to Chinese engineering. Today, visitors can explore the wall's impressive 12m-high gates, battlements and bulwarks. One of the best preserved gates of the wall, Zhonghua Men, also distinguishes itself as the largest castle in China.