Daniel 6:7-9

All the royal administrators, prefects, satraps, advisers, and governors have agreed that the king should establish an ordinance and enforce a decree that for thirty days anyone who petitions any god or man except you, O king, will be thrown into the den of lions.

Therefore, O king, establish the decree and sign the document so that it cannot be changed—in accordance with the law of the Medes and Persians, which cannot be repealed.”

Therefore King Darius signed the written decree.