Charles Ellicott Commentary Daniel 6:17

"And a stone was brought, and laid upon the mouth of the den; and the king sealed it with his own signet, and with the signet of his lords; that nothing might be changed concerning Daniel." — Daniel 6:17 (ASV)

Sealed it. —This sealing by both the king and his nobles appears to have been due to the fear that the nobles had (Daniel 6:16) that the king might attempt to rescue Daniel. The nobles also would be unable to put Daniel to death if he escaped the fury of the lions.