Charles Ellicott Commentary Daniel 6:16

"Then the king commanded, and they brought Daniel, and cast him into the den of lions. [Now] the king spake and said unto Daniel, Thy God whom thou servest continually, he will deliver thee." — Daniel 6:16 (ASV)

They brought Daniel.— According to Eastern custom, the sentence was generally executed on the day when it was pronounced. This explains why the king’s efforts to commute the sentence were prolonged till sunset (Daniel 6:14). The lions were probably kept here for sporting purposes. The form of the den is unknown, but the etymology suggests a vaulted chamber.