Jiayuguan Fort, Gansu, China — The westernmost substantial fort of the Ming Great Wall stood at the edge of the Gobi Desert and was known as the 'First and Greatest Pass under Heaven.' Caravans on the Silk Road passed through its gates, and exiled officials bade farewell to civilization here as they departed into the barbarian west.
© Adolf Nikolay Boyarsky, Public domain, via Wikimedia Commons
