After centuries, walls that once protected mighty emperors are beginning to show their age. The walls of the ancient imperial center of power that is now the Palace Museum in Beijing have weaknesses like loose bricks and bulging, cracking surfaces.

On Saturday, the museum, also known as the Forbidden City, began a restoration project to keep the walls from collapsing.

"People usually think the walls are much more solid than our wooden palace architecture," said Shan Jixiang, director of the museum. "However, the result of our detailed investigation has told us they are not."