A new mapping study shows that the great wall is longer than was previously thought. From the BBC:
A two-year government mapping study found that the wall spans 8,850km (5,500 miles) – until now, the length was commonly put at about 5,000km.
Previous estimates of its length were mainly based on historical records.
Infra-red and GPS technologies helped locate some areas concealed over time by sandstorms, state media said.