Abstract: A cap unit for a retaining wall constructed of a plurality of courses of concrete blocks, in which at least the uppermost course of blocks in the retaining wall is provided with a connector member having an upstanding portion extending above the upper surface of the block, is provided with a recess or cavity in its underside for receiving the upstanding portion of the connector member. The cap unit is constructed such that the upstanding portion of the connector member abuts a side of the cavity so as to prevent lateral forward movement of the cap unit relative to the block therebelow. The cavity comprises a slot extending the width of the cap unit to accommodate varying placements of the connector member relative to the cap unit. The cap unit is formed so as to provide first and second end surfaces substantially parallel to each other, with a first side surface extending therebetween. The first side surface is perpendicular to both the first and second end surfaces.