According to a new survey, the Great Wall of China is up to a third longer than previously estimated: during the Ming Dynasty, the wall was not a mere 6,000 kilomtres long, but stretched for at least 8,851.8 kilometres.A team of researchers spent two years mapping the wall using GPS positioning systems and infra-red technology to build up the most comprehensive picture of the wall to date. Only some short stretches of the Great Wall have been fully restored. In many other areas it has disappeared completely. It remains however a focus of much national pride. The surveying team now plan more hi-tech research into the Qin and Han dynasty sections of the Great Wall. The research programme is due to be completed next year.