Easton's Bible Dictionary: M. G. Easton, M.A., D.D.
A lair of wild beasts (Ps. 10:9, 104:22; Job 37:8); the hole of a venomous reptile (Isa. 11:8); a recess for secrecy "in dens and caves of the earth" (Heb. 11:38); a resort of thieves (Mt. 21:13; Mk. 11:17). Daniel was cast into "the den of lions" (Dan. 6:16, 17). Some recent discoveries among the ruins of Babylon have brought to light the fact that the practice of punishing offenders against the law by throwing them into a den of lions was common.