The Grand Canal of China is the longest canal or artificial river in the world, stretching over 1,776 kilometers from Beijing to Hangzhou. Parts of it date back to the 5th century BC, but it was largely connected during the Sui Dynasty (581–618 AD). It was built to transport grain from the fertile Yangtze River delta to the imperial capital in the north. The canal features an ingenious ancient engineering feat known as the 'pound lock,' which was invented in China in 984 AD to help boats navigate changes in water levels—centuries before they appeared in Europe. Today, while some sections are silted up, much of it remains a working industrial waterway and a UNESCO World Heritage site representing the peak of ancient hydraulic engineering.