A robotic device movable in a vertical direction between rails arranged in multiple rows at various levels with respect to ground. The robotic device has a frame, wheels coupled to the frame for moving the frame along the rails, and a movable platform provided on the frame. The platform is configured for moving the frame in a vertical direction between first rails and second rails arranged above the first rails, and for placing onto the robotic device first and second loads arranged at different levels with respect to the ground.