A building element for a set of toy building elements that are capable of being interconnected in a releasable engagement includes side walls having grooves and tongues, a top having a broad surface that extends toward the side walls and a primarily cylindrical projection extending above the broad surface; a open bottom; and an interior having a plurality of ribs with contact surfaces that are accessible through the open bottom and disposed for interconnecting with the projection on the top of another such building element. At least some of the contact surfaces of the interior ribs include lateral indentations; and the projection includes a circular lateral ridge disposed above the broad surface for being interconnected in a releasable restaining engagement within the indentations in the interior contact surfaces of the ribs of another such building element. The tongues in the side walls are adapted for interconnecting in a releasable restraining engagement within a groove in a side wall of another such building element.