As the only existent county-level ancient city wall in China, Pingyao City Wall was originally built between 827 - 782 BC during the reign of King Xuan of the Western Zhou Dynasty (11th Century - 771BC). In the early years of the Ming Dynasty (1368 - 1644), it was renovated and extended to protect central China against invasions from other nationalities. Different from other city walls in China, there are totally 6 gates garrisoned by 6 Wongcheng on the wall, which form an enormous tortoise, so it is also called tortoise city.