In this study, optimum design of cantilever reinforced concrete cantilever retaining walls is investigated under static load conditions. A methodology based on a recently developed metaheuristic algorithm called grey wolf optimizer was proposed. As the objective function, the total cost of the retaining wall including concrete, steel, labor, transportation etc. is considered. The eleven design variables such as heel and toe projections, stem thickness at the top and bottom of the wall, slab thickness, diameters and spacing of reinforced bars in critical sections are considered in the optimization process. During the optimization, totally twenty-nine design constraints including overturning stability, sliding stability, bearing capacity (max...