The City Wall of Xi’an is the most complete one that has survived in China. Xi’an served as China’s capital for more than 1,100 years and 13 imperial dynasties. During the Tang years (618-907) it was the largest city in the world. It was during the Ming Dynasty that construction of the City Wall began in the year 1370. It encircles the city center of 14 square kilometers (5.4 square miles). The wall measures 8.5 miles in length, 49 to 59 feet in thickness at the base and 39 feet in height. The exterior of the wall is surrounded by a moat and each city gate has three gate towers. The width is 40 to 46 feet at the top and it can be traversed by foot, bike or rubber-wheeled buses for those who don’t want that much exercise.