Then these men assembled unto the king, and said unto the king, Know, O king, that the law of the Medes and Persians is, That no decree nor statute which the king establishes may be changed.
All Commentaries on Daniel 6:15 Go To Daniel 6
Jerome
AD 420
Just as the king understood that the princes were making their accusation out of motives of envy, so also they for their part understood what the king's purpose was, namely that he wished to rescue Daniel from imminent death. And so they allege that according to the law of the Medes and Persians, the commands of a king cannot be nullified.