The ruins of a 2,000-year-old walled city have been found in a reservoir on China's north-east border with North Korea, exposed when the water level in the Yunfeng reservoir was lowered for repairs. The Xinhua news agency said the ruins, near the city of Ji'an, were believed to date from China's Han dynasty of 202BC to 220. The city also included tombs of Koguryo design from Korea. The ruined city's wall, surrounded by a moat, is 1.5 metres (5ft) high and four metres thick, and encloses an area 180 metres by 220 metres. The dam and reservoir were built in the 1950s.