Abstract: An element for constructing a structure by detachably connecting a plurality of the elements in edge-to-edge relationship is disclosed. The element comprises a plurality of margins, with at least one of the margins being an arcuate margin. Each margin comprises at least two projections having a recess therebetween. An end-face of one projection is formed with a protruding hinge-pip and an end-face of the other or another projection is formed with a recessed hinge-socket. The arcuate margin is adapted to mate with a complementary margin of another element with the hinge-pip of each element being urged into the hinge socket of the other element.