Large swaths of the Great Wall of China are held together thanks to "biocrusts," thin layers of organic materials that have helped protect the architectural marvel from erosion.
Scientists made the discovery while analyzing segments of the Great Wall of China, which spans more than 13,000 miles (21,000 kilometers) and was built over the course of many centuries, beginning in 221 B.C., as a way to protect the country's empires from the outside world.
