An ancient irrigation system that dates back 4,000 years has been unearthed in Chengdu of southwest China's Sichuan Province, according to the city's municipal museum on Thursday. The system, with a 147-meter-long bank protection dam, was discovered at a real estate construction site in Wenjiang District of the city. The dam is 14 meters wide at the bottom, 12 meters at the top and 1.3 meters high with eight grooves dug by hand. Five house relics and 54 tombs were discovered on the east side of the dam, which proved that the dam was built to protect the community, according to the museum. The dam is the earliest irrigation system in the areas along the upper reaches of the Yangtze River, said Wang Yi, curator of the museum. It is 2,000 years older than the Dujiangyan irrigation system, also near Chengdu and a world cultural heritage site, he said.