Jiayu Pass in Gansu province

Jiayu Pass or  Jiayuguan  (simplified Chinese: 嘉峪关; traditional Chinese: 嘉峪關;pinyin: Jiāyù Guān; literally: "Excellent Valley Pass") is the first pass at the west end of theGreat Wall of China, near the city of Jiayuguanin Gansu province. Along with Juyong Passand Shanhai Pass, it is one of the main passes of the Great Wall. The structure lies between two hills, one of which is called Jiayuguan Pass. It was built near an oasis that was then on the extreme western edge of China.

The structure was built during the early Ming dynasty, sometime around the year 1372. The fortress there was greatly strengthened due to fear of an invasion by Timur, but Timur died of old age while leading an army toward China. There are two gates: one on the east side of the pass and the other on the west side. On each gate there is a building. An inscription of "Jiayuguan" in Chinese is written on a tablet at the building at the west gate. The south and north sides of the pass are connected to the Great Wall. There is a turret on each corner of the pass. On the north side, inside the two gates, there are wide roads leading to the top of the pass. 

A fabulous legend recounts the meticulous planning involved in the construction of the pass. According to legend, when Jiayuguan was being planned, the official in charge asked the designer to estimate the exact number of bricks required and the designer gave him a number (99,999). The official questioned his judgment, asking him if that would be enough, so the designer added one brick. When Jiayuguan was finished, there was one brick left over, which was placed loose on one of the gates where it remains today.

Picture Source: Collected from Internet