Precast concrete modules for stacked assembly into a retaining wall have rectangular face panels and single retaining stems connected to rear faces of the face panels. Each retaining stem includes a slot or other device for receiving a stabilizing web that extends transversely between the stems of modules arranged side-by-side in a horizontal row. The single retaining stem of each module may be connected to the rear face of the module at a location spaced from one side edge of the face panel by one quarter of the distance between opposite side edge of the panel. A retaining wall assembly includes modules stacked in successive courses, with the face panels being staggered in adjacent courses to create a "brick bonded" stack, and with the retaining stems of modules in successive courses being superposed in vertical alignment.