Easton's Bible Dictionary: M. G. Easton, M.A., D.D.
Cities were surrounded by walls, as distinguished from "unwalled villages" (Ezek. 38:11; Lev. 25:29-34). They were made thick and strong (Num. 13:28; Dt. 3:5). Among the Jews walls were built of stone, some of those in the temple being of great size (1 Ki. 6:7, 7:9-12, 20:30; Mk. 13:1, 2). The term is used metaphorically of security and safety (Isa. 26:1, 60:18; Rev. 21:12-20).