Tuntian (屯田) were military-agricultural colonies that supplied grain to the state and army. Cao Cao implemented the system in the early 200s on the advice of Zao Zhi and Han Hao, after seeing the supply difficulties that had weakened Yuan Shao and Yuan Shu.
Role under Cao Cao
Settling soldiers and refugees on state land shortened supply lines, increased grain production, and gave war-ravaged regions a way to recover. Cao Cao appointed officers such as Zao Zhi to run the colonies; the tuntian system became a lasting feature of Wei administration. It was eventually abolished under Cao Huan in 264.