Xiadu, also known as the Lower Capital of Yan, was a significant historical city located in China. It served as one of the primary capitals of the state of Yan during the Warring States period of ancient Chinese history.
The city is notable for its historical scale and size. From approximately 400 to 300 BC, Xiadu may have been the largest city in the world, reaching an estimated peak population of over 300,000 residents.