Answer:
1. The official length is 21,196.18 km (13,170.7 mi) —; (6+ dynasties' worth)
2. Most of today's relics are the Ming Dynasty Great Wall: length 8,851 km (5,500 mi).
3. The Great Wall is more than 2,300 years old.
4. The Ming Great Wall crosses 9 provinces and municipalities: Liaoning, Hebei, Tianjin, Beijing, Inner Mongolia, Shanxi, Shaanxi, Ningxia, Gansu.
5. Badaling is the most visited section (63,000,000 visitors in 2001). And in the first week of May and October, the visitor flow can be up to 70,000 per day.