Jiayuguan

Jiayu Pass or is the first frontier fortress at the west end of the Ming dynasty Great Wall, near the city of Jiayuguan in Gansu province. Along with Juyong Pass and Shanhai Pass, it is one of the main passes of the Great Wall. In the Ming period, foreign merchants and envoys from the Central Asia and West Asia mostly entered China through Jiayu Pass.
Data from: en.wikipedia.org