Coordinates: Tongwancheng (Chinese: ; pinyin: ) was the capital of the Xia kingdom, a kingdom founded by the Xiongnu in northern China during the Sixteen Kingdoms period in the early 5th century. The city is at the southern edge of the Maowusu Sands of the Ordos Desert, on what was formerly a strategic site in the centre of the Ordos Plateau. Tongwancheng, which means the "city ruling ten thousand", is the largest urban center of the Southern Xiongnu that has ever been found. The city's ruins are well preserved and located in Jingbian County, Shaanxi Province, near the border with Inner Mongolia. The city has been surveyed and some elements restored, but not yet fully excavated.
The city was built by around 100,000 Xiongnu of the Xia kingdom under the command of Helian Bobo in 419. Helian Bobo, also known by his sinified surname as Liu Bobo, was a descendant of the Xiongnu chanyu who founded their steppe empire in the 3rd century BC. Helian Bobo died in 425 AD, and Helian Chang succeeded him as ruler of the city.
The Great Wall of China was built to contain the Xiongnu threat, and Tongwancheng was the main Xiongnu capital that stood on other side of that wall. The city was largely of wood construction and had very thick outer walls which were made white with white clay earth and powdered rice. From a distance the white city was said to have had the appearance of a giant ship. At its centre the city had a lake. Jin Shu gives us a contemporary eyewitness description of the city...
At its height the population was around 10,000, likely to have been greatly supplemented by an encircling encampment of nomadic kin groups at certain times of the year. White cities were generally ceremonial and status centres built following conquest, rather than outright military positions, white being a blessed colour for the Xiongnu. Yet the thickness of the walls was certainly required since the city was originally built at a time of perpetual warfare. The threat was also internal as well as from the Chinese - for instance, Helian Bobo was attacked with an army by his deputy Helian Gui in 424 following a dynastic dispute.
In 426, the Emperor Taiwu of Northern Wei made a surprise attack on Tongwancheng. Although a brief incursion into the city succeeded only in burning the main temple, the surrounding hinterland was devastated. The city's site was on the fertile upper reaches of the Wuding River, but the river and lake died up, possibly due to deforestation that might be traced back to Taiwu's devastation. The city was then gradually buried by the sands of the desert. This 'wandering' (Wuding) gave the river its current name.
The Xiongnu continued to live in the region until the 7th or 8th century. In 786 the city was besieged by Tibetan forces, and it was invaded by Jurchen soldiers in 1206. There is no record of the site in Chinese records after the early 15th century.
The city was only properly surveyed by the Chinese in the 2000s. The city's Yong'an Platform, a military forces inspection platform for dignitaries, has been restored.
The city is also referred to in the literature variously as Tong Wan Cheng, Tongwan-cheng, Tongwan, Xia Zhou, Baichengzi (Chinese: ; Wade-Giles: Pai-cheng-tzu), or Bai Cheng (; 'White City').