A seawall is formed of concrete modules that are laterally disposed relative to one another and interlocked to one another at their abutting end walls. Each module has a base that overlies a support surface and an upstanding sea-retaining wall disposed perpendicular to the base, forming an inverted "T" and having no brace walls. The sea-retaining wall has a front surface facing a body of water and a back surface facing land. The seawall is formed by a mold that includes a base having a generally parallelepiped configuration and a pair of slightly inclined mold walls for forming the sea-retaining wall of the module. A first embodiment includes a steel mold. A second embodiment includes an aluminum mold having parts that open along hinge lines and which require reinforcement dowels to prevent pressure-induced bulges.