The Four Seas (Chinese: 四海; pinyin: Sìhǎi) were four bodies of water that metaphorically made up the boundaries of ancient China.

[1] Two of the seas were symbolic until they were tied to genuine locations during the Han dynasty's wars with the Xiongnu.

Jia Yi, in an essay that summarized the collapse of Qin dynasty, wrote that while the state of Qin has succeeded in "pocketing all within the Four Seas, and swallowing up everything in all Eight Directions", its ruler "lacked humaneness and rightness; because preserving power differs fundamentally from seizing power".

[4] The metaphor is also referenced in the Chinese adage "we are all brothers of the Four Seas", a proverb with utopian undercurrents.

The lyrics of a popular Han dynasty folk song extol that "within the Four Seas, we are all brothers, and none be taken as strangers!