In ancient times prisoners were packed into wooden cages and escorted to the capital.
Tips
history
Historically a wooden cage on a cart used to transport prisoners - vivid in classical novels like 水浒传, where rebels are paraded in 囚笼. Modern usage is mostly figurative: a marriage, a job, or a bureaucracy can be one's 囚笼.
memory
囚 itself is a person (人) inside an enclosure (囗) - a built-in pictograph for 'imprisoned'. Add 笼 (cage) and you've doubled down on the confinement.
