Some ground units are "civil units", having no attack strength and therefore unable to enter unguarded foreign cities. Those that have attack strength ("weapons"), for which the minimum is 4, are "military units". All must have at least some defensive strength ("armor"). Each unit has a maximum "speed", the distance it can normally travel in one turn. The minimum is 1.5 (i.e., one diagonal step - N, S, E, or W on an isometric map - that's not using a road or river).