The danger of enslavement to warlike individuals bent on conquest was another compelling reason for fearful people to band together into cities. They invariably fenced in and walled up these cities, and they closed the gateways at night and in times of danger.​—Jos 2:5; 2Ch 26:6.

Since defense was generally of prime importance, ancient cities were usually placed on high elevations. Though this exposed them to open view, they were difficult to reach. (Mt 5:14) Coastal cities and those along the banks of rivers were exceptions. In addition to the natural barriers, often massive walls or a complex of walls and towers and, in some instances, moats were built around the city. (2Ki 9:17; Ne 3:1–4:23; 6:1-15; Da 9:25) As cities grew, it was sometimes necessary to extend the walls to include greater perimeters. Entrances through the walls were secured with strong gates that could withstand prolonged siege. (See FORTIFICATIONS; GATE, GATEWAY; WALLS.) Outside and beyond the walls were the fields, pasture grounds, and suburbs that were often undefended during attack.​—Nu 35:1-8; Jos 21:41, 42.

A good nearby water supply was absolutely essential and not to be overlooked when selecting a site for a city. For this reason it was counted ideal when cities had springs or wells enclosed within their limits. In certain instances, notably Megiddo, Gibeon, and Jerusalem, there were underground water tunnels and conduits to bring water inside the walls from sources outside. (2Sa 5:8; 2Ki 20:20; 2Ch 32:30) Reservoirs and cisterns were often constructed for catching and holding water during the wet season for use at a later time. In some instances the terrain was honeycombed with cisterns, as each household endeavored to have its own supply of water.​—2Ch 26:10.