Since its beginnings, the Chinese civilisation has been linked to water control and irrigation. The milestones in the construction of canals for irrigation, transport and flood control have accompanied the long history of this civilisation, the oldest that has come down to us and one of the longest in history.
Today, some experts have considered that the building of the Three Gorges Dam, the largest in the world, is a sign of the relocation of China in their traditional central position in the world, as the Middle Kingdom once was. But the Three Gorges, though being one of the world's largest water infrastructures, may not be so representative of the close historical relationship between China and water management as the ancient Karez irrigation system, known as "The Underground Great Wall". The building of this complex irrigation system, with a total length of 5,000 km, began at least 2,000 years ago to take advantage of melt water and rain from the Tiansan mountains in northwest China, and it is still used today, having undergone careful restoration.