In 2007, a stone inscription of the construction of the Great Wall in the Sui Dynasty was discovered in Kelan County, Shanxi Province. This Great Wall construction inscription is the earliest construction inscription with a date found so far. According to a survey in 2009, the remains of the Great Wall of the Sui Dynasty are located on the top of the mountain. They are made of stone and have collapsed into a rocky beach. They are about 50 to 80 centimeters high. The Great Wall on the mountainside is made of earth. The remaining height on the surface is about 1.5 meters, and the rammed earth layer is 13 centimeters.