An armor module is the design feature of a C-evo unit that gives it defensive strength. The basic value/strength of an armor module depends on the knowledge of relevant technologies and is proportionally reduced if the unit's health is below 100%. For units in a city, defensive strength is halved for naval units and zero for air units. Factors that may increase strength come from buildings and terrain. Every new unit design must incorporate at least one armor module. Players can add more, up to specified limits, depending on the weight limit and (again) the knowledge of relevant technologies.