Abstract: The invention is a set of construction elements in which each element is open-ended and comprises four identical wall sections. Each wall section is a quarter cylinder. The elements have two basic forms; one in which the four wall sections are disposed outwardly convex, and the element is an open-ended cylinder; and the other in which the four wall sections are disposed outwardly concave, and the element has a curvilinear square section. Horizontal rows are constructed by alternately arranging the cylindrical and curvilinear square elements. Walls are erected by superposing horizontal rows. The superposed rows can be offset relative to one another, and the thus-exposed open tops of the rows filled with soil to serve as flower beds. Preferably, each element has vertical channels formed on the exterior surface of the wall sections, in which connecting rods can be seated so as to interconnect adjacent horizontal and vertical elements.