Easton's Bible Dictionary: M. G. Easton, M.A., D.D.
The materials of which gates were made were,
At the gates of cities courts of justice were frequently held, and hence "judges of the gate" are spoken of (Dt. 16:18, 17:8, 21:19, 25:6, 7, etc.). At the gates prophets also frequently delivered their messages (Pr. 1:21, 8:3; Isa. 29:21; Jer. 17:19, 20, 26:10). Criminals were punished without the gates (1 Ki. 21:13; Acts 7:59). By the "gates of righteousness" we are probably to understand those of the temple (Ps. 118:19). "The gates of hell" (R.V., "gates of Hades") Mt. 16:18, are generally interpreted as meaning the power of Satan, but probably they may mean the power of death, denoting that the Church of Christ shall never die.