Toward the end of the Warring States period (475–221 BC), the powerful state of Qin sought to annex its rivals and unify China. In 228 BC, after conquering a neighboring state, Qin prepared to invade Yan. In desperation, Prince Dan of Yan dispatched a brave warrior named Jing Ke to assassinate the King of Qin.
To gain the king's trust, Jing Ke brought a map of Yan's most fertile lands as a tribute, concealing a sharp dagger within its scroll. Admitted to the palace, he respectfully presented the map when ordered. As he slowly unrolled it before the king, the hidden dagger was revealed at the scroll's end. Jing Ke seized it and lunged at the king, who dodged the attack and hid behind a large pillar. The assassin was swiftly overpowered and killed by the palace guards, and his mission failed. Subsequently, Qin conquered and wiped out Yan.
This story gave rise to the idiom "the dagger unrolled," which means one's true, often hostile, intentions are finally revealed.